Message-ID: <125a8efc-da13-a08f-8218-76e6167634d7@ghiti.fr>
Date:   Fri, 10 Feb 2023 14:24:17 +0100
From:   Alexandre Ghiti <alex@...ti.fr>
To:     JeeHeng Sia <jeeheng.sia@...rfivetech.com>,
        "paul.walmsley@...ive.com" <paul.walmsley@...ive.com>,
        "palmer@...belt.com" <palmer@...belt.com>,
        "aou@...s.berkeley.edu" <aou@...s.berkeley.edu>
Cc:     "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Leyfoon Tan <leyfoon.tan@...rfivetech.com>,
        Mason Huo <mason.huo@...rfivetech.com>
Subject: Re: [PATCH v3 4/4] RISC-V: Add arch functions to support
 hibernation/suspend-to-disk

On 2/9/23 07:12, JeeHeng Sia wrote:
> Hi Alex,
>
>> -----Original Message-----
>> From: Alexandre Ghiti <alex@...ti.fr>
>> Sent: Wednesday, 8 February, 2023 8:05 PM
>> To: JeeHeng Sia <jeeheng.sia@...rfivetech.com>; paul.walmsley@...ive.com; palmer@...belt.com; aou@...s.berkeley.edu
>> Cc: linux-riscv@...ts.infradead.org; linux-kernel@...r.kernel.org; Leyfoon Tan <leyfoon.tan@...rfivetech.com>; Mason Huo
>> <mason.huo@...rfivetech.com>
>> Subject: Re: [PATCH v3 4/4] RISC-V: Add arch functions to support hibernation/suspend-to-disk
>>
>> Hi Sia,
>>
>> On 2/8/23 05:43, JeeHeng Sia wrote:
>>>> -----Original Message-----
>>>> From: Alexandre Ghiti <alex@...ti.fr>
>>>> Sent: Tuesday, 7 February, 2023 11:46 PM
>>>> To: JeeHeng Sia <jeeheng.sia@...rfivetech.com>; paul.walmsley@...ive.com; palmer@...belt.com; aou@...s.berkeley.edu
>>>> Cc: linux-riscv@...ts.infradead.org; linux-kernel@...r.kernel.org; Leyfoon Tan <leyfoon.tan@...rfivetech.com>; Mason Huo
>>>> <mason.huo@...rfivetech.com>
>>>> Subject: Re: [PATCH v3 4/4] RISC-V: Add arch functions to support hibernation/suspend-to-disk
>>>>
>>>> Hi Sia,
>>>>
>>>> On 1/27/23 10:10, Sia Jee Heng wrote:
>>>>> Low level Arch functions were created to support hibernation.
>>>>> swsusp_arch_suspend() relies code from __cpu_suspend_enter() to write
>>>>> cpu state onto the stack, then calling swsusp_save() to save the memory
>>>>> image.
>>>>>
>>>>> Arch specific hibernation header is implemented and is utilized by the
>>>>> arch_hibernation_header_restore() and arch_hibernation_header_save()
>>>>> functions. The arch specific hibernation header consists of satp, hartid,
>>>>> and the cpu_resume address. The kernel built version is also need to be
>>>>> saved into the hibernation image header to making sure only the same
>>>>> kernel is restore when resume.
>>>>>
>>>>> swsusp_arch_resume() creates a temporary page table that covering only
>>>>> the linear map. It copies the restore code to a 'safe' page, then start
>>>>> to restore the memory image. Once completed, it restores the original
>>>>> kernel's page table. It then calls into __hibernate_cpu_resume()
>>>>> to restore the CPU context. Finally, it follows the normal hibernation
>>>>> path back to the hibernation core.
>>>>>
>>>>> To enable hibernation/suspend to disk into RISCV, the below config
>>>>> need to be enabled:
>>>>> - CONFIG_ARCH_HIBERNATION_HEADER
>>>>> - CONFIG_ARCH_HIBERNATION_POSSIBLE
>>>>>
>>>>> Signed-off-by: Sia Jee Heng <jeeheng.sia@...rfivetech.com>
>>>>> Reviewed-by: Ley Foon Tan <leyfoon.tan@...rfivetech.com>
>>>>> Reviewed-by: Mason Huo <mason.huo@...rfivetech.com>
>>>>> ---
>>>>>     arch/riscv/Kconfig                 |   7 +
>>>>>     arch/riscv/include/asm/assembler.h |  20 ++
>>>>>     arch/riscv/include/asm/suspend.h   |  21 ++
>>>>>     arch/riscv/kernel/Makefile         |   1 +
>>>>>     arch/riscv/kernel/asm-offsets.c    |   5 +
>>>>>     arch/riscv/kernel/hibernate-asm.S  |  89 +++++++
>>>>>     arch/riscv/kernel/hibernate.c      | 360 +++++++++++++++++++++++++++++
>>>>>     7 files changed, 503 insertions(+)
>>>>>     create mode 100644 arch/riscv/kernel/hibernate-asm.S
>>>>>     create mode 100644 arch/riscv/kernel/hibernate.c
>>>>>
>>>>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>>>>> index e2b656043abf..4555848a817f 100644
>>>>> --- a/arch/riscv/Kconfig
>>>>> +++ b/arch/riscv/Kconfig
>>>>> @@ -690,6 +690,13 @@ menu "Power management options"
>>>>>
>>>>>     source "kernel/power/Kconfig"
>>>>>
>>>>> +config ARCH_HIBERNATION_POSSIBLE
>>>>> +	def_bool y
>>>>> +
>>>>> +config ARCH_HIBERNATION_HEADER
>>>>> +	def_bool y
>>>>> +	depends on HIBERNATION
>>>>> +
>>>>>     endmenu # "Power management options"
>>>>>
>>>>>     menu "CPU Power Management"
>>>>> diff --git a/arch/riscv/include/asm/assembler.h b/arch/riscv/include/asm/assembler.h
>>>>> index ef1283d04b70..3de70d3e6ceb 100644
>>>>> --- a/arch/riscv/include/asm/assembler.h
>>>>> +++ b/arch/riscv/include/asm/assembler.h
>>>>> @@ -59,4 +59,24 @@
>>>>>     		REG_L	s11, (SUSPEND_CONTEXT_REGS + PT_S11)(a0)
>>>>>     	.endm
>>>>>
>>>>> +/**
>>>>> + * copy_page - copy 1 page (4KB) of data from source to destination
>>>>> + * @a0 - destination
>>>>> + * @a1 - source
>>>>> + */
>>>>> +	.macro	copy_page a0, a1
>>>>> +		lui	a2, 0x1
>>>>> +		add	a2, a2, a0
>>>>> +.1 :
>>>>> +		REG_L	t0, 0(a1)
>>>>> +		REG_L	t1, SZREG(a1)
>>>>> +
>>>>> +		REG_S	t0, 0(a0)
>>>>> +		REG_S	t1, SZREG(a0)
>>>>> +
>>>>> +		addi	a0, a0, 2 * SZREG
>>>>> +		addi	a1, a1, 2 * SZREG
>>>>> +		bne	a2, a0, .1
>>>>> +	.endm
>>>>> +
>>>>>     #endif	/* __ASM_ASSEMBLER_H */
>>>>> diff --git a/arch/riscv/include/asm/suspend.h b/arch/riscv/include/asm/suspend.h
>>>>> index 75419c5ca272..db40ae433aa9 100644
>>>>> --- a/arch/riscv/include/asm/suspend.h
>>>>> +++ b/arch/riscv/include/asm/suspend.h
>>>>> @@ -21,6 +21,12 @@ struct suspend_context {
>>>>>     #endif
>>>>>     };
>>>>>
>>>>> +/*
>>>>> + * This parameter will be assigned to 0 during resume and will be used by
>>>>> + * hibernation core for the subsequent resume sequence
>>>>> + */
>>>>> +extern int in_suspend;
>>>>> +
>>>>>     /* Low-level CPU suspend entry function */
>>>>>     int __cpu_suspend_enter(struct suspend_context *context);
>>>>>
>>>>> @@ -36,4 +42,19 @@ int __cpu_resume_enter(unsigned long hartid, unsigned long context);
>>>>>     /* Used to save and restore the csr */
>>>>>     void suspend_save_csrs(struct suspend_context *context);
>>>>>     void suspend_restore_csrs(struct suspend_context *context);
>>>>> +
>>>>> +/* Low-level API to support hibernation */
>>>>> +int swsusp_arch_suspend(void);
>>>>> +int swsusp_arch_resume(void);
>>>>> +int arch_hibernation_header_save(void *addr, unsigned int max_size);
>>>>> +int arch_hibernation_header_restore(void *addr);
>>>>> +int __hibernate_cpu_resume(void);
>>>>> +
>>>>> +/* Used to resume on the CPU we hibernated on */
>>>>> +int hibernate_resume_nonboot_cpu_disable(void);
>>>>> +
>>>>> +/* Used to restore the hibernated image */
>>>>> +asmlinkage void restore_image(unsigned long resume_satp, unsigned long satp_temp,
>>>>> +				unsigned long cpu_resume);
>>>>> +asmlinkage int core_restore_code(void);
>>>>>     #endif
>>>>> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
>>>>> index 4cf303a779ab..daab341d55e4 100644
>>>>> --- a/arch/riscv/kernel/Makefile
>>>>> +++ b/arch/riscv/kernel/Makefile
>>>>> @@ -64,6 +64,7 @@ obj-$(CONFIG_MODULES)		+= module.o
>>>>>     obj-$(CONFIG_MODULE_SECTIONS)	+= module-sections.o
>>>>>
>>>>>     obj-$(CONFIG_CPU_PM)		+= suspend_entry.o suspend.o
>>>>> +obj-$(CONFIG_HIBERNATION)	+= hibernate.o hibernate-asm.o
>>>>>
>>>>>     obj-$(CONFIG_FUNCTION_TRACER)	+= mcount.o ftrace.o
>>>>>     obj-$(CONFIG_DYNAMIC_FTRACE)	+= mcount-dyn.o
>>>>> diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c
>>>>> index df9444397908..d6a75aac1d27 100644
>>>>> --- a/arch/riscv/kernel/asm-offsets.c
>>>>> +++ b/arch/riscv/kernel/asm-offsets.c
>>>>> @@ -9,6 +9,7 @@
>>>>>     #include <linux/kbuild.h>
>>>>>     #include <linux/mm.h>
>>>>>     #include <linux/sched.h>
>>>>> +#include <linux/suspend.h>
>>>>>     #include <asm/kvm_host.h>
>>>>>     #include <asm/thread_info.h>
>>>>>     #include <asm/ptrace.h>
>>>>> @@ -116,6 +117,10 @@ void asm_offsets(void)
>>>>>
>>>>>     	OFFSET(SUSPEND_CONTEXT_REGS, suspend_context, regs);
>>>>>
>>>>> +	OFFSET(HIBERN_PBE_ADDR, pbe, address);
>>>>> +	OFFSET(HIBERN_PBE_ORIG, pbe, orig_address);
>>>>> +	OFFSET(HIBERN_PBE_NEXT, pbe, next);
>>>>> +
>>>>>     	OFFSET(KVM_ARCH_GUEST_ZERO, kvm_vcpu_arch, guest_context.zero);
>>>>>     	OFFSET(KVM_ARCH_GUEST_RA, kvm_vcpu_arch, guest_context.ra);
>>>>>     	OFFSET(KVM_ARCH_GUEST_SP, kvm_vcpu_arch, guest_context.sp);
>>>>> diff --git a/arch/riscv/kernel/hibernate-asm.S b/arch/riscv/kernel/hibernate-asm.S
>>>>> new file mode 100644
>>>>> index 000000000000..a83d534b89bd
>>>>> --- /dev/null
>>>>> +++ b/arch/riscv/kernel/hibernate-asm.S
>>>>> @@ -0,0 +1,89 @@
>>>>> +/* SPDX-License-Identifier: GPL-2.0-only */
>>>>> +/*
>>>>> + * Hibernation support specific for RISCV
>>>>> + *
>>>>> + * Copyright (C) 2023 StarFive Technology Co., Ltd.
>>>>> + *
>>>>> + * Author: Jee Heng Sia <jeeheng.sia@...rfivetech.com>
>>>>> + */
>>>>> +
>>>>> +#include <asm/asm.h>
>>>>> +#include <asm/asm-offsets.h>
>>>>> +#include <asm/assembler.h>
>>>>> +#include <asm/csr.h>
>>>>> +
>>>>> +#include <linux/linkage.h>
>>>>> +
>>>>> +/*
>>>>> + * This code is executed when resume from the hibernation.
>>>>> + *
>>>>> + * It begins with loading the temporary page table then restores the memory image.
>>>>> + * Finally branches to __hibernate_cpu_resume() to restore the state saved by
>>>>> + * swsusp_arch_suspend().
>>>>> + */
>>>>> +
>>>>> +/*
>>>>> + * int __hibernate_cpu_resume(void)
>>>>> + * Switch back to the hibernated image's page table prior to restore the CPU
>>>>> + * context.
>>>>> + *
>>>>> + * Always returns 0 to the C code.
>>>>> + */
>>>>> +ENTRY(__hibernate_cpu_resume)
>>>>> +	/* switch to hibernated image's page table */
>>>>> +	csrw CSR_SATP, s0
>>>>> +	sfence.vma
>>>>> +
>>>>> +	REG_L	a0, hibernate_cpu_context
>>>>> +
>>>>> +	/* Restore CSRs */
>>>>> +	restore_csr
>>>>> +
>>>>> +	/* Restore registers (except A0 and T0-T6) */
>>>>> +	restore_reg
>>>>> +
>>>>> +	/* Return zero value */
>>>>> +	add	a0, zero, zero
>>>>> +
>>>>> +	/* Return to C code */
>>>>> +	ret
>>>>> +END(__hibernate_cpu_resume)
>>>>> +
>>>>> +/*
>>>>> + * Prepare to restore the image.
>>>>> + * a0: satp of saved page tables
>>>>> + * a1: satp of temporary page tables
>>>>> + * a2: cpu_resume
>>>>> + */
>>>>> +ENTRY(restore_image)
>>>>> +	mv	s0, a0
>>>>> +	mv	s1, a1
>>>>> +	mv	s2, a2
>>>>> +	REG_L	s4, restore_pblist
>>>>> +	REG_L	a1, relocated_restore_code
>>>>> +
>>>>> +	jalr	a1
>>>>> +END(restore_image)
>>>>> +
>>>>> +/*
>>>>> + * The below code will be executed from a 'safe' page.
>>>>> + * It first switches to the temporary page table, then start to copy the pages
>>>>> + * back to the original memory location. Finally, it jumps to the __hibernate_cpu_resume()
>>>>> + * to restore the CPU context.
>>>>> + */
>>>>> +ENTRY(core_restore_code)
>>>>> +	/* switch to temp page table */
>>>>> +	csrw satp, s1
>>>>> +	sfence.vma
>>>>> +.Lcopy:
>>>>> +	/* The below code will restore the hibernated image. */
>>>>> +	REG_L	a1, HIBERN_PBE_ADDR(s4)
>>>>> +	REG_L	a0, HIBERN_PBE_ORIG(s4)
>>>>> +
>>>>> +	copy_page a0, a1
>>>>> +
>>>>> +	REG_L	s4, HIBERN_PBE_NEXT(s4)
>>>>> +	bnez	s4, .Lcopy
>>>>> +
>>>>> +	jalr	s2
>>>>> +END(core_restore_code)
>>>>> diff --git a/arch/riscv/kernel/hibernate.c b/arch/riscv/kernel/hibernate.c
>>>>> new file mode 100644
>>>>> index 000000000000..bf7f3c781820
>>>>> --- /dev/null
>>>>> +++ b/arch/riscv/kernel/hibernate.c
>>>>> @@ -0,0 +1,360 @@
>>>>> +// SPDX-License-Identifier: GPL-2.0-only
>>>>> +/*
>>>>> + * Hibernation support specific for RISCV
>>>>> + *
>>>>> + * Copyright (C) 2023 StarFive Technology Co., Ltd.
>>>>> + *
>>>>> + * Author: Jee Heng Sia <jeeheng.sia@...rfivetech.com>
>>>>> + */
>>>>> +
>>>>> +#include <asm/barrier.h>
>>>>> +#include <asm/cacheflush.h>
>>>>> +#include <asm/mmu_context.h>
>>>>> +#include <asm/page.h>
>>>>> +#include <asm/pgtable.h>
>>>>> +#include <asm/sections.h>
>>>>> +#include <asm/set_memory.h>
>>>>> +#include <asm/smp.h>
>>>>> +#include <asm/suspend.h>
>>>>> +
>>>>> +#include <linux/cpu.h>
>>>>> +#include <linux/memblock.h>
>>>>> +#include <linux/pm.h>
>>>>> +#include <linux/sched.h>
>>>>> +#include <linux/suspend.h>
>>>>> +#include <linux/utsname.h>
>>>>> +
>>>>> +/* The logical cpu number we should resume on, initialised to a non-cpu number */
>>>>> +static int sleep_cpu = -EINVAL;
>>>>> +
>>>>> +/* CPU context to be saved */
>>>>> +struct suspend_context *hibernate_cpu_context;
>>>>> +
>>>>> +unsigned long relocated_restore_code;
>>>>> +
>>>>> +/* Pointer to the temporary resume page table */
>>>>> +pgd_t *resume_pg_dir;
>>>>> +
>>>>> +/**
>>>>> + * struct arch_hibernate_hdr_invariants - container to store kernel build version
>>>>> + * @uts_version: to save the build number and date so that the we are not resume with
>>>>> + *		a different kernel
>>>>> + */
>>>>> +struct arch_hibernate_hdr_invariants {
>>>>> +	char		uts_version[__NEW_UTS_LEN + 1];
>>>>> +};
>>>>> +
>>>>> +/**
>>>>> + * struct arch_hibernate_hdr - helper parameters that help us to restore the image
>>>>> + * @invariants: container to store kernel build version
>>>>> + * @hartid: to make sure same boot_cpu executing the hibernate/restore code.
>>>>> + * @saved_satp: original page table used by the hibernated image.
>>>>> + * @restore_cpu_addr: the kernel's image address to restore the CPU context.
>>>>> + */
>>>>> +static struct arch_hibernate_hdr {
>>>>> +	struct arch_hibernate_hdr_invariants invariants;
>>>>> +	unsigned long	hartid;
>>>>> +	unsigned long	saved_satp;
>>>>> +	unsigned long	restore_cpu_addr;
>>>>> +} resume_hdr;
>>>>> +
>>>>> +static inline void arch_hdr_invariants(struct arch_hibernate_hdr_invariants *i)
>>>>> +{
>>>>> +	memset(i, 0, sizeof(*i));
>>>>> +	memcpy(i->uts_version, init_utsname()->version, sizeof(i->uts_version));
>>>>> +}
>>>>> +
>>>>> +/*
>>>>> + * Check if the given pfn is in the 'nosave' section.
>>>>> + */
>>>>> +int pfn_is_nosave(unsigned long pfn)
>>>>> +{
>>>>> +	unsigned long nosave_begin_pfn = sym_to_pfn(&__nosave_begin);
>>>>> +	unsigned long nosave_end_pfn = sym_to_pfn(&__nosave_end - 1);
>>>>> +
>>>>> +	return ((pfn >= nosave_begin_pfn) && (pfn <= nosave_end_pfn));
>>>>> +}
>>>>> +
>>>>> +void notrace save_processor_state(void)
>>>>> +{
>>>>> +	WARN_ON(num_online_cpus() != 1);
>>>>> +}
>>>>> +
>>>>> +void notrace restore_processor_state(void)
>>>>> +{
>>>>> +}
>>>>> +
>>>>> +/*
>>>>> + * Helper parameters need to be saved to the hibernation image header.
>>>>> + */
>>>>> +int arch_hibernation_header_save(void *addr, unsigned int max_size)
>>>>> +{
>>>>> +	struct arch_hibernate_hdr *hdr = addr;
>>>>> +
>>>>> +	if (max_size < sizeof(*hdr))
>>>>> +		return -EOVERFLOW;
>>>>> +
>>>>> +	arch_hdr_invariants(&hdr->invariants);
>>>>> +
>>>>> +	hdr->hartid = cpuid_to_hartid_map(sleep_cpu);
>>>>> +	hdr->saved_satp = csr_read(CSR_SATP);
>>>>> +	hdr->restore_cpu_addr = (unsigned long)__hibernate_cpu_resume;
>>>>> +
>>>>> +	return 0;
>>>>> +}
>>>>> +EXPORT_SYMBOL(arch_hibernation_header_save);
>>>>> +
>>>>> +/*
>>>>> + * Retrieve the helper parameters from the hibernation image header
>>>>> + */
>>>>> +int arch_hibernation_header_restore(void *addr)
>>>>> +{
>>>>> +	struct arch_hibernate_hdr_invariants invariants;
>>>>> +	struct arch_hibernate_hdr *hdr = addr;
>>>>> +	int ret = 0;
>>>>> +
>>>>> +	arch_hdr_invariants(&invariants);
>>>>> +
>>>>> +	if (memcmp(&hdr->invariants, &invariants, sizeof(invariants))) {
>>>>> +		pr_crit("Hibernate image not generated by this kernel!\n");
>>>>> +		return -EINVAL;
>>>>> +	}
>>>>> +
>>>>> +	sleep_cpu = riscv_hartid_to_cpuid(hdr->hartid);
>>>>> +	if (sleep_cpu < 0) {
>>>>> +		pr_crit("Hibernated on a CPU not known to this kernel!\n");
>>>>> +		sleep_cpu = -EINVAL;
>>>>> +		return -EINVAL;
>>>>> +	}
>>>>> +
>>>>> +#ifdef CONFIG_SMP
>>>>> +	ret = bringup_hibernate_cpu(sleep_cpu);
>>>>> +	if (ret) {
>>>>> +		sleep_cpu = -EINVAL;
>>>>> +		return ret;
>>>>> +	}
>>>>> +#endif
>>>>> +	resume_hdr = *hdr;
>>>>> +
>>>>> +	return ret;
>>>>> +}
>>>>> +EXPORT_SYMBOL(arch_hibernation_header_restore);
>>>>> +
>>>>> +int swsusp_arch_suspend(void)
>>>>> +{
>>>>> +	int ret = 0;
>>>>> +
>>>>> +	if (__cpu_suspend_enter(hibernate_cpu_context)) {
>>>>> +		sleep_cpu = smp_processor_id();
>>>>> +		suspend_save_csrs(hibernate_cpu_context);
>>>>> +		ret = swsusp_save();
>>>>> +	} else {
>>>>> +		suspend_restore_csrs(hibernate_cpu_context);
>>>>> +		flush_tlb_all();
>>>>> +
>>>>> +		/* Invalidated Icache */
>>>>> +		flush_icache_all();
>>>>> +
>>>>> +		/*
>>>>> +		 * Tell the hibernation core that we've just restored
>>>>> +		 * the memory
>>>>> +		 */
>>>>> +		in_suspend = 0;
>>>>> +		sleep_cpu = -EINVAL;
>>>>> +	}
>>>>> +
>>>>> +	return ret;
>>>>> +}
>>>>> +
>>>>> +static unsigned long temp_pgtable_map_pte(pte_t *ptep, unsigned long vaddr, pgprot_t prot)
>>>>> +{
>>>>> +	uintptr_t pte_idx = pte_index(vaddr);
>>>>> +
>>>>> +	ptep[pte_idx] = pfn_pte(PFN_DOWN(__pa(vaddr)), prot);
>>>>> +
>>>>> +	return 0;
>>>>> +}
>>>>> +
>>>>> +#ifndef __PAGETABLE_PMD_FOLDED
>>>>> +#define temp_pgtable_map_pgd_next(pgdp, vaddr, prot)			\
>>>>> +		(pgtable_l5_enabled ?					\
>>>>> +		temp_pgtable_map_p4d(pgdp, vaddr, prot) :		\
>>>>> +		(pgtable_l4_enabled ?					\
>>>>> +		temp_pgtable_map_pud((pud_t *)pgdp, vaddr, prot) :	\
>>>>> +		temp_pgtable_map_pmd((pmd_t *)pgdp, vaddr, prot)))
>>>>> +
>>>>> +static unsigned long temp_pgtable_map_pmd(pmd_t *pmdp, unsigned long vaddr, pgprot_t prot)
>>>>> +{
>>>>> +	uintptr_t pmd_idx = pmd_index(vaddr);
>>>>> +	pte_t *ptep;
>>>>> +
>>>>> +	if (pmd_none(pmdp[pmd_idx])) {
>>>>> +		ptep = (pte_t *)get_safe_page(GFP_ATOMIC);
>>>>> +		if (!ptep)
>>>>> +			return -ENOMEM;
>>>>> +
>>>>> +		memset(ptep, 0, PAGE_SIZE);
>>>>> +		pmdp[pmd_idx] = pfn_pmd(PFN_DOWN(__pa(ptep)), PAGE_TABLE);
>>>>> +	} else {
>>>>> +		ptep = (pte_t *)__va(PFN_PHYS(_pmd_pfn(pmdp[pmd_idx])));
>>>>> +	}
>>>>> +
>>>>> +	return temp_pgtable_map_pte(ptep, vaddr, prot);
>>>>> +}
>>>>> +
>>>>> +static unsigned long temp_pgtable_map_pud(pud_t *pudp, unsigned long vaddr, pgprot_t prot)
>>>>> +{
>>>>> +	uintptr_t pud_index = pud_index(vaddr);
>>>>> +	pmd_t *pmdp;
>>>>> +
>>>>> +	if (pud_val(pudp[pud_index]) == 0) {
>>>>> +		pmdp = (pmd_t *)get_safe_page(GFP_ATOMIC);
>>>>> +		if (!pmdp)
>>>>> +			return -ENOMEM;
>>>>> +
>>>>> +		memset(pmdp, 0, PAGE_SIZE);
>>>>> +		pudp[pud_index] = pfn_pud(PFN_DOWN(__pa(pmdp)), PAGE_TABLE);
>>>>> +	} else {
>>>>> +		pmdp = (pmd_t *)__va(PFN_PHYS(_pud_pfn(pudp[pud_index])));
>>>>> +	}
>>>>> +
>>>>> +	return temp_pgtable_map_pmd(pmdp, vaddr, prot);
>>>>> +}
>>>>> +
>>>>> +static unsigned long temp_pgtable_map_p4d(p4d_t *p4dp, unsigned long vaddr, pgprot_t prot)
>>>>> +{
>>>>> +	uintptr_t p4d_index = p4d_index(vaddr);
>>>>> +	pud_t *pudp;
>>>>> +
>>>>> +	if (p4d_val(p4dp[p4d_index]) == 0) {
>>>>> +		pudp = (pud_t *)get_safe_page(GFP_ATOMIC);
>>>>> +		if (!pudp)
>>>>> +			return -ENOMEM;
>>>>> +
>>>>> +		memset(pudp, 0, PAGE_SIZE);
>>>>> +		p4dp[p4d_index] = pfn_p4d(PFN_DOWN(__pa(pudp)), PAGE_TABLE);
>>>>> +	} else {
>>>>> +		pudp = (pud_t *)__va(PFN_PHYS(_p4d_pfn(p4dp[p4d_index])));
>>>>> +	}
>>>>> +
>>>>> +	return temp_pgtable_map_pud(pudp, vaddr, prot);
>>>>> +}
>>>>> +
>>>>> +#else
>>>>> +#define temp_pgtable_map_pgd_next(nextp, vaddr, prot)	\
>>>>> +	temp_pgtable_map_pte((pte_t *)nextp, vaddr, prot)
>>>>> +#endif /* __PAGETABLE_PMD_FOLDED */
>>>>> +
>>>>> +static unsigned long temp_pgtable_map_pgd(pgd_t *pgdp, unsigned long vaddr, pgprot_t prot)
>>>>> +{
>>>>> +	uintptr_t pgd_idx = pgd_index(vaddr);
>>>>> +	void *nextp;
>>>>> +
>>>>> +	if (pgd_val(pgdp[pgd_idx]) == 0) {
>>>>> +		nextp = (void *)get_safe_page(GFP_ATOMIC);
>>>>> +		if (!nextp)
>>>>> +			return -ENOMEM;
>>>>> +
>>>>> +		memset(nextp, 0, PAGE_SIZE);
>>>>> +		pgdp[pgd_idx] = pfn_pgd(PFN_DOWN(__pa(nextp)), PAGE_TABLE);
>>>>> +	} else {
>>>>> +		nextp = (void *)__va(PFN_PHYS(_pgd_pfn(pgdp[pgd_idx])));
>>>>> +	}
>>>>> +
>>>>> +	return temp_pgtable_map_pgd_next(nextp, vaddr, prot);


Is it possible to use "standard" way of going through a page table 
instead of using the _next macros? I mean something like this (example 
from arm64 code 
https://elixir.bootlin.com/linux/latest/source/arch/arm64/mm/trans_pgd.c#L174 
or my recent kasan patchset 
https://patchwork.kernel.org/project/linux-riscv/patch/20230203075232.274282-3-alexghiti@rivosinc.com/):

         do {
                 next = pgd_addr_end(vaddr, end);

                 if (pgd_none(*pgd_k)) {
                         nextp = get_safe_page(GFP_ATOMIC);
                         memset(nextp, 0, PAGE_SIZE);
                         set_pgd(pgd_k, pfn_pgd(PFN_DOWN(__pa(nextp)), 
PAGE_TABLE));
continue;
}

                 kasan_shallow_populate_p4d(pgd_k, vaddr, next);
         } while (pgd_k++, vaddr = next, vaddr != end);


I have the same change to our early page table code on my todo list.


>>>>> +}
>>>>> +
>>>>> +static unsigned long temp_pgtable_mapping(pgd_t *pgdp, unsigned long vaddr, pgprot_t prot)
>>>>> +{
>>>>> +	return temp_pgtable_map_pgd(pgdp, vaddr, prot);
>>>>> +}
>>>>> +
>>>>> +static unsigned long relocate_restore_code(void)
>>>>> +{
>>>>> +	unsigned long ret;
>>>>> +	void *page = (void *)get_safe_page(GFP_ATOMIC);
>>>>> +
>>>>> +	if (!page)
>>>>> +		return -ENOMEM;
>>>>> +
>>>>> +	copy_page(page, core_restore_code);
>>>>> +
>>>>> +	/* Make the page containing the relocated code executable */
>>>>> +	set_memory_x((unsigned long)page, 1);
>>>>> +
>>>>> +	ret = temp_pgtable_mapping(resume_pg_dir, (unsigned long)page, PAGE_KERNEL_READ_EXEC);
>>>>> +	if (ret)
>>>>> +		return ret;
>>>>> +
>>>>> +	return (unsigned long)page;
>>>>> +}
>>>>> +
>>>>> +int swsusp_arch_resume(void)
>>>>> +{
>>>>> +	unsigned long addr = PAGE_OFFSET;
>>>>> +	unsigned long ret;
>>>>> +
>>>>> +	/*
>>>>> +	 * Memory allocated by get_safe_page() will be dealt with by the hibernation core,
>>>>> +	 * we don't need to free it here.
>>>>> +	 */
>>>>> +	resume_pg_dir = (pgd_t *)get_safe_page(GFP_ATOMIC);
>>>>> +	if (!resume_pg_dir)
>>>>> +		return -ENOMEM;
>>>>> +
>>>>> +	/*
>>>>> +	 * The pages need to be writable when restoring the image.
>>>>> +	 * Create a second copy of page table just for the linear map, and use this when
>>>>> +	 * restoring.
>>>>> +	 */
>>>>> +	for (; addr <= (unsigned long)pfn_to_virt(max_low_pfn); addr += PAGE_SIZE) {
>>>>> +		ret = temp_pgtable_mapping(resume_pg_dir, addr, PAGE_KERNEL);
>>>>> +		if (ret)
>>>>> +			return (int)ret;
>>>>> +	}
>>>>> +
>>>> To me this is wrong as this does not account for the real physical
>>>> mapping layout: can't you simply copy the linear mapping from
>>>> swapper_pg_dir?
>>> Hi, we covering the linear mapping from PAGE_OFFSET up to pfn_to_virt(max_low_pfn). We shouldn't copy from the
>> swapper_pg_dir as we are not suppose to modify its content.
>>
>>
>> First, you're right, we need the temporary page table as swapper_pg_dir
>> will get overwritten under our feet.
>>
>> Now, I still disagree with mapping all the memory: the linear mapping is
>> sparse because we only map what memblock gives us (some regions are
>> marked as "nomap" for a reason).
>>
>> I just took a look at arm64, and they do exactly that: they go through
>> swapper_pg_dir, copy the linear mapping and enable write at every leaf
>> level
>> (https://elixir.bootlin.com/linux/latest/source/arch/arm64/kernel/hibernate.c#L419).
> You're right, but we don’t have to copy from the swapper_pg_dir. We can insert kernel_page_present() to the function to check the page validity prior to do the mapping. Agree?


That would work, we'd lose the benefit of huge pages though, I'm not 
opposed at all but if we can leverage existing arm64 code, that would 
even be better, only the PTE write flag is different!

Thanks,

Alex


>>
>>>> But I have to admit that I struggle to understand the need for this
>>>> temporary page table: all we need to do is to allow to write to the
>>>> linear mapping, so why don't we simply set_memory_rw(linear mapping)?
>>> Similar to the above comment. When we restore the memory content, we need to make sure the pages are write-able. if you modify
>> the swapper_pg_dir, the kernel will crash afterwards.
>>> That’s why we need a second page table to do the recovering job.
>>>>> +	/* Move the restore code to a new page so that it doesn't get overwritten by itself */
>>>>> +	relocated_restore_code = relocate_restore_code();
>>>> And do we really need to do that too? The code in question can only be
>>>> overwritten by the same code right?
>>> Yes, we need to move the recovering code to a new page to prevent the code from overwrite itself when restoring the memory.
>>>> Thanks,
>>>>
>>>> Alex
>>>>
>>>>
>>>>> +	if (relocated_restore_code == -ENOMEM)
>>>>> +		return -ENOMEM;
>>>>> +
>>>>> +	/*
>>>>> +	 * Map the __hibernate_cpu_resume() address to the temporary page table so that the
>>>>> +	 * restore code can jump to it after finished restore the image. The next execution
>>>>> +	 * code doesn't find itself in a different address space after switching over to the
>>>>> +	 * original page table used by the hibernated image.
>>>>> +	 */
>>>>> +	ret = temp_pgtable_mapping(resume_pg_dir, (unsigned long)resume_hdr.restore_cpu_addr,
>>>>> +					PAGE_KERNEL_READ_EXEC);
>>>>> +	if (ret)
>>>>> +		return ret;
>>>>> +
>>>>> +	restore_image(resume_hdr.saved_satp, (PFN_DOWN(__pa(resume_pg_dir)) | satp_mode),
>>>>> +			resume_hdr.restore_cpu_addr);
>>>>> +
>>>>> +	return 0;
>>>>> +}
>>>>> +
>>>>> +#ifdef CONFIG_PM_SLEEP_SMP
>>>>> +int hibernate_resume_nonboot_cpu_disable(void)
>>>>> +{
>>>>> +	if (sleep_cpu < 0) {
>>>>> +		pr_err("Failing to resume from hibernate on an unknown CPU.\n");
>>>>> +		return -ENODEV;
>>>>> +	}
>>>>> +
>>>>> +	return freeze_secondary_cpus(sleep_cpu);
>>>>> +}
>>>>> +#endif
>>>>> +
>>>>> +static int __init riscv_hibernate_init(void)
>>>>> +{
>>>>> +	hibernate_cpu_context = kcalloc(1, sizeof(struct suspend_context), GFP_KERNEL);
>>>>> +
>>>>> +	if (WARN_ON(!hibernate_cpu_context))
>>>>> +		return -ENOMEM;
>>>>> +
>>>>> +	return 0;
>>>>> +}
>>>>> +
>>>>> +early_initcall(riscv_hibernate_init);
>>> _______________________________________________
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