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Message-ID: <c83f82a9-8981-2fee-867e-17ae5dba3f0d@loongson.cn>
Date: Tue, 23 Dec 2025 10:35:08 +0800
From: lixianglai <lixianglai@...ngson.cn>
To: Bibo Mao <maobibo@...ngson.cn>, loongarch@...ts.linux.dev,
linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc: stable@...r.kernel.org, Huacai Chen <chenhuacai@...nel.org>,
WANG Xuerui <kernel@...0n.name>, Tianrui Zhao <zhaotianrui@...ngson.cn>,
Charlie Jenkins <charlie@...osinc.com>, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH V2 1/2] LoongArch: KVM: Compile the switch.S file directly
into the kernel
Hi Bibo Mao:
>
>
> On 2025/12/22 下午7:34, Xianglai Li wrote:
>> If we directly compile the switch.S file into the kernel, the address of
>> the kvm_exc_entry function will definitely be within the DMW memory
>> area.
>> Therefore, we will no longer need to perform a copy relocation of
>> kvm_exc_entry.
>>
>> Based on the above description, compile switch.S directly into the
>> kernel,
>> and then remove the copy relocation execution logic for the
>> kvm_exc_entry
>> function.
>>
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Xianglai Li <lixianglai@...ngson.cn>
>> ---
>> Cc: Huacai Chen <chenhuacai@...nel.org>
>> Cc: WANG Xuerui <kernel@...0n.name>
>> Cc: Tianrui Zhao <zhaotianrui@...ngson.cn>
>> Cc: Bibo Mao <maobibo@...ngson.cn>
>> Cc: Charlie Jenkins <charlie@...osinc.com>
>> Cc: Xianglai Li <lixianglai@...ngson.cn>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>>
>> arch/loongarch/Kbuild | 2 +-
>> arch/loongarch/include/asm/asm-prototypes.h | 21 +++++++++++++
>> arch/loongarch/include/asm/kvm_host.h | 3 --
>> arch/loongarch/kvm/Makefile | 2 +-
>> arch/loongarch/kvm/main.c | 35 ++-------------------
>> arch/loongarch/kvm/switch.S | 22 ++++++++++---
>> 6 files changed, 43 insertions(+), 42 deletions(-)
>>
>> diff --git a/arch/loongarch/Kbuild b/arch/loongarch/Kbuild
>> index beb8499dd8ed..1c7a0dbe5e72 100644
>> --- a/arch/loongarch/Kbuild
>> +++ b/arch/loongarch/Kbuild
>> @@ -3,7 +3,7 @@ obj-y += mm/
>> obj-y += net/
>> obj-y += vdso/
>> -obj-$(CONFIG_KVM) += kvm/
>> +obj-$(subst m,y,$(CONFIG_KVM)) += kvm/
>> # for cleaning
>> subdir- += boot
>> diff --git a/arch/loongarch/include/asm/asm-prototypes.h
>> b/arch/loongarch/include/asm/asm-prototypes.h
>> index 704066b4f736..e8ce153691e5 100644
>> --- a/arch/loongarch/include/asm/asm-prototypes.h
>> +++ b/arch/loongarch/include/asm/asm-prototypes.h
>> @@ -20,3 +20,24 @@ asmlinkage void noinstr __no_stack_protector
>> ret_from_kernel_thread(struct task_
>> struct pt_regs *regs,
>> int (*fn)(void *),
>> void *fn_arg);
>> +
>> +struct kvm_run;
>> +struct kvm_vcpu;
>> +
>> +void kvm_exc_entry(void);
>> +int kvm_enter_guest(struct kvm_run *run, struct kvm_vcpu *vcpu);
>> +
>> +struct loongarch_fpu;
>> +
>> +#ifdef CONFIG_CPU_HAS_LSX
>> +void kvm_save_lsx(struct loongarch_fpu *fpu);
>> +void kvm_restore_lsx(struct loongarch_fpu *fpu);
>> +#endif
>> +
>> +#ifdef CONFIG_CPU_HAS_LASX
>> +void kvm_save_lasx(struct loongarch_fpu *fpu);
>> +void kvm_restore_lasx(struct loongarch_fpu *fpu);
>> +#endif
>> +
>> +void kvm_save_fpu(struct loongarch_fpu *fpu);
>> +void kvm_restore_fpu(struct loongarch_fpu *fpu);
>> diff --git a/arch/loongarch/include/asm/kvm_host.h
>> b/arch/loongarch/include/asm/kvm_host.h
>> index e4fe5b8e8149..1a1be10e3803 100644
>> --- a/arch/loongarch/include/asm/kvm_host.h
>> +++ b/arch/loongarch/include/asm/kvm_host.h
>> @@ -85,7 +85,6 @@ struct kvm_context {
>> struct kvm_world_switch {
>> int (*exc_entry)(void);
>> int (*enter_guest)(struct kvm_run *run, struct kvm_vcpu *vcpu);
>> - unsigned long page_order;
>> };
>> #define MAX_PGTABLE_LEVELS 4
>> @@ -347,8 +346,6 @@ void kvm_exc_entry(void);
>> int kvm_enter_guest(struct kvm_run *run, struct kvm_vcpu *vcpu);
>> extern unsigned long vpid_mask;
>> -extern const unsigned long kvm_exception_size;
>> -extern const unsigned long kvm_enter_guest_size;
>> extern struct kvm_world_switch *kvm_loongarch_ops;
>> #define SW_GCSR (1 << 0)
>> diff --git a/arch/loongarch/kvm/Makefile b/arch/loongarch/kvm/Makefile
>> index cb41d9265662..fe665054f824 100644
>> --- a/arch/loongarch/kvm/Makefile
>> +++ b/arch/loongarch/kvm/Makefile
>> @@ -11,7 +11,7 @@ kvm-y += exit.o
>> kvm-y += interrupt.o
>> kvm-y += main.o
>> kvm-y += mmu.o
>> -kvm-y += switch.o
>> +obj-y += switch.o
>> kvm-y += timer.o
>> kvm-y += tlb.o
>> kvm-y += vcpu.o
>> diff --git a/arch/loongarch/kvm/main.c b/arch/loongarch/kvm/main.c
>> index 80ea63d465b8..67d234540ed4 100644
>> --- a/arch/loongarch/kvm/main.c
>> +++ b/arch/loongarch/kvm/main.c
>> @@ -340,8 +340,7 @@ void kvm_arch_disable_virtualization_cpu(void)
>> static int kvm_loongarch_env_init(void)
>> {
>> - int cpu, order, ret;
>> - void *addr;
>> + int cpu, ret;
>> struct kvm_context *context;
>> vmcs = alloc_percpu(struct kvm_context);
>> @@ -357,30 +356,8 @@ static int kvm_loongarch_env_init(void)
>> return -ENOMEM;
>> }
>> - /*
>> - * PGD register is shared between root kernel and kvm hypervisor.
>> - * So world switch entry should be in DMW area rather than TLB area
>> - * to avoid page fault reenter.
>> - *
>> - * In future if hardware pagetable walking is supported, we won't
>> - * need to copy world switch code to DMW area.
>> - */
>> - order = get_order(kvm_exception_size + kvm_enter_guest_size);
>> - addr = (void *)__get_free_pages(GFP_KERNEL, order);
>> - if (!addr) {
>> - free_percpu(vmcs);
>> - vmcs = NULL;
>> - kfree(kvm_loongarch_ops);
>> - kvm_loongarch_ops = NULL;
>> - return -ENOMEM;
>> - }
>> -
>> - memcpy(addr, kvm_exc_entry, kvm_exception_size);
>> - memcpy(addr + kvm_exception_size, kvm_enter_guest,
>> kvm_enter_guest_size);
>> - flush_icache_range((unsigned long)addr, (unsigned long)addr +
>> kvm_exception_size + kvm_enter_guest_size);
>> - kvm_loongarch_ops->exc_entry = addr;
>> - kvm_loongarch_ops->enter_guest = addr + kvm_exception_size;
>> - kvm_loongarch_ops->page_order = order;
>> + kvm_loongarch_ops->exc_entry = (void *)kvm_exc_entry;
>> + kvm_loongarch_ops->enter_guest = (void *)kvm_enter_guest;
>> vpid_mask = read_csr_gstat();
>> vpid_mask = (vpid_mask & CSR_GSTAT_GIDBIT) >>
>> CSR_GSTAT_GIDBIT_SHIFT;
>> @@ -414,16 +391,10 @@ static int kvm_loongarch_env_init(void)
>> static void kvm_loongarch_env_exit(void)
>> {
>> - unsigned long addr;
>> -
>> if (vmcs)
>> free_percpu(vmcs);
>> if (kvm_loongarch_ops) {
>> - if (kvm_loongarch_ops->exc_entry) {
>> - addr = (unsigned long)kvm_loongarch_ops->exc_entry;
>> - free_pages(addr, kvm_loongarch_ops->page_order);
>> - }
>> kfree(kvm_loongarch_ops);
>> }
>> diff --git a/arch/loongarch/kvm/switch.S b/arch/loongarch/kvm/switch.S
>> index f1768b7a6194..93845ce53651 100644
>> --- a/arch/loongarch/kvm/switch.S
>> +++ b/arch/loongarch/kvm/switch.S
>> @@ -5,6 +5,7 @@
>> #include <linux/linkage.h>
>> #include <asm/asm.h>
>> +#include <asm/page.h>
>> #include <asm/asmmacro.h>
>> #include <asm/loongarch.h>
>> #include <asm/regdef.h>
>> @@ -100,10 +101,18 @@
>> * - is still in guest mode, such as pgd table/vmid
>> registers etc,
>> * - will fix with hw page walk enabled in future
>> * load kvm_vcpu from reserved CSR KVM_VCPU_KS, and save a2 to
>> KVM_TEMP_KS
>> + *
>> + * PGD register is shared between root kernel and kvm hypervisor.
>> + * So world switch entry should be in DMW area rather than TLB area
>> + * to avoid page fault reenter.
>> + *
>> + * In future if hardware pagetable walking is supported, we won't
>> + * need to copy world switch code to DMW area.
>> */
>> .text
>> .cfi_sections .debug_frame
>> SYM_CODE_START(kvm_exc_entry)
>> + .p2align PAGE_SHIFT
>> UNWIND_HINT_UNDEFINED
>> csrwr a2, KVM_TEMP_KS
>> csrrd a2, KVM_VCPU_KS
>> @@ -190,8 +199,8 @@ ret_to_host:
>> kvm_restore_host_gpr a2
>> jr ra
>> -SYM_INNER_LABEL(kvm_exc_entry_end, SYM_L_LOCAL)
>> SYM_CODE_END(kvm_exc_entry)
>> +EXPORT_SYMBOL(kvm_exc_entry)
>> /*
>> * int kvm_enter_guest(struct kvm_run *run, struct kvm_vcpu *vcpu)
>> @@ -215,8 +224,8 @@ SYM_FUNC_START(kvm_enter_guest)
>> /* Save kvm_vcpu to kscratch */
>> csrwr a1, KVM_VCPU_KS
>> kvm_switch_to_guest
>> -SYM_INNER_LABEL(kvm_enter_guest_end, SYM_L_LOCAL)
>> SYM_FUNC_END(kvm_enter_guest)
>> +EXPORT_SYMBOL(kvm_enter_guest)
>> SYM_FUNC_START(kvm_save_fpu)
>> fpu_save_csr a0 t1
>> @@ -224,6 +233,7 @@ SYM_FUNC_START(kvm_save_fpu)
>> fpu_save_cc a0 t1 t2
>> jr ra
>> SYM_FUNC_END(kvm_save_fpu)
>> +EXPORT_SYMBOL(kvm_save_fpu)
> one small nit, could EXPORT_SYMBOL_FOR_KVM() be used here compared
> with EXPORT_SYMBOL()?
>
Ok! will fix it in next version
Thanks!
Xianglai.
> Regards
> Bibo Mao
>> SYM_FUNC_START(kvm_restore_fpu)
>> fpu_restore_double a0 t1
>> @@ -231,6 +241,7 @@ SYM_FUNC_START(kvm_restore_fpu)
>> fpu_restore_cc a0 t1 t2
>> jr ra
>> SYM_FUNC_END(kvm_restore_fpu)
>> +EXPORT_SYMBOL(kvm_restore_fpu)
>> #ifdef CONFIG_CPU_HAS_LSX
>> SYM_FUNC_START(kvm_save_lsx)
>> @@ -239,6 +250,7 @@ SYM_FUNC_START(kvm_save_lsx)
>> lsx_save_data a0 t1
>> jr ra
>> SYM_FUNC_END(kvm_save_lsx)
>> +EXPORT_SYMBOL(kvm_save_lsx)
>> SYM_FUNC_START(kvm_restore_lsx)
>> lsx_restore_data a0 t1
>> @@ -246,6 +258,7 @@ SYM_FUNC_START(kvm_restore_lsx)
>> fpu_restore_csr a0 t1 t2
>> jr ra
>> SYM_FUNC_END(kvm_restore_lsx)
>> +EXPORT_SYMBOL(kvm_restore_lsx)
>> #endif
>> #ifdef CONFIG_CPU_HAS_LASX
>> @@ -255,6 +268,7 @@ SYM_FUNC_START(kvm_save_lasx)
>> lasx_save_data a0 t1
>> jr ra
>> SYM_FUNC_END(kvm_save_lasx)
>> +EXPORT_SYMBOL(kvm_save_lasx)
>> SYM_FUNC_START(kvm_restore_lasx)
>> lasx_restore_data a0 t1
>> @@ -262,10 +276,8 @@ SYM_FUNC_START(kvm_restore_lasx)
>> fpu_restore_csr a0 t1 t2
>> jr ra
>> SYM_FUNC_END(kvm_restore_lasx)
>> +EXPORT_SYMBOL(kvm_restore_lasx)
>> #endif
>> - .section ".rodata"
>> -SYM_DATA(kvm_exception_size, .quad kvm_exc_entry_end - kvm_exc_entry)
>> -SYM_DATA(kvm_enter_guest_size, .quad kvm_enter_guest_end -
>> kvm_enter_guest)
>> #ifdef CONFIG_CPU_HAS_LBT
>> STACK_FRAME_NON_STANDARD kvm_restore_fpu
>>
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