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Message-ID: <20230123142554.f22ajf6upfk2ybxk@orel>
Date: Mon, 23 Jan 2023 15:25:54 +0100
From: Andrew Jones <ajones@...tanamicro.com>
To: Alexandre Ghiti <alexghiti@...osinc.com>
Cc: Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>, Guo Ren <guoren@...nel.org>,
Rob Herring <robh+dt@...nel.org>,
Frank Rowand <frowand.list@...il.com>,
linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
devicetree@...r.kernel.org, linux-arch@...r.kernel.org,
Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v4] riscv: Use PUD/P4D/PGD pages for the linear mapping
On Mon, Jan 23, 2023 at 12:28:02PM +0100, Alexandre Ghiti wrote:
> During the early page table creation, we used to set the mapping for
> PAGE_OFFSET to the kernel load address: but the kernel load address is
> always offseted by PMD_SIZE which makes it impossible to use PUD/P4D/PGD
> pages as this physical address is not aligned on PUD/P4D/PGD size (whereas
> PAGE_OFFSET is).
>
> But actually we don't have to establish this mapping (ie set va_pa_offset)
> that early in the boot process because:
>
> - first, setup_vm installs a temporary kernel mapping and among other
> things, discovers the system memory,
> - then, setup_vm_final creates the final kernel mapping and takes
> advantage of the discovered system memory to create the linear
> mapping.
>
> During the first phase, we don't know the start of the system memory and
> then until the second phase is finished, we can't use the linear mapping at
> all and phys_to_virt/virt_to_phys translations must not be used because it
> would result in a different translation from the 'real' one once the final
> mapping is installed.
>
> So here we simply delay the initialization of va_pa_offset to after the
> system memory discovery. But to make sure noone uses the linear mapping
> before, we add some guard in the DEBUG_VIRTUAL config.
>
> Finally we can use PUD/P4D/PGD hugepages when possible, which will result
> in a better TLB utilization.
>
> Note that we rely on the firmware to protect itself using PMP.
>
> Acked-by: Rob Herring <robh@...nel.org> # DT bits
> Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
> ---
>
> v4:
> - Rebase on top of v6.2-rc3, as noted by Conor
> - Add Acked-by Rob
>
> v3:
> - Change the comment about initrd_start VA conversion so that it fits
> ARM64 and RISCV64 (and others in the future if needed), as suggested
> by Rob
>
> v2:
> - Add a comment on why RISCV64 does not need to set initrd_start/end that
> early in the boot process, as asked by Rob
>
> arch/riscv/include/asm/page.h | 16 ++++++++++++++++
> arch/riscv/mm/init.c | 25 +++++++++++++++++++------
> arch/riscv/mm/physaddr.c | 16 ++++++++++++++++
> drivers/of/fdt.c | 11 ++++++-----
> 4 files changed, 57 insertions(+), 11 deletions(-)
>
> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> index 9f432c1b5289..7fe84c89e572 100644
> --- a/arch/riscv/include/asm/page.h
> +++ b/arch/riscv/include/asm/page.h
> @@ -90,6 +90,14 @@ typedef struct page *pgtable_t;
> #define PTE_FMT "%08lx"
> #endif
>
> +#ifdef CONFIG_64BIT
> +/*
> + * We override this value as its generic definition uses __pa too early in
> + * the boot process (before kernel_map.va_pa_offset is set).
> + */
> +#define MIN_MEMBLOCK_ADDR 0
> +#endif
> +
> #ifdef CONFIG_MMU
> extern unsigned long riscv_pfn_base;
> #define ARCH_PFN_OFFSET (riscv_pfn_base)
> @@ -122,7 +130,11 @@ extern phys_addr_t phys_ram_base;
> #define is_linear_mapping(x) \
> ((x) >= PAGE_OFFSET && (!IS_ENABLED(CONFIG_64BIT) || (x) < PAGE_OFFSET + KERN_VIRT_SIZE))
>
> +#ifndef CONFIG_DEBUG_VIRTUAL
> #define linear_mapping_pa_to_va(x) ((void *)((unsigned long)(x) + kernel_map.va_pa_offset))
> +#else
> +void *linear_mapping_pa_to_va(unsigned long x);
> +#endif
> #define kernel_mapping_pa_to_va(y) ({ \
> unsigned long _y = (unsigned long)(y); \
> (IS_ENABLED(CONFIG_XIP_KERNEL) && _y < phys_ram_base) ? \
> @@ -131,7 +143,11 @@ extern phys_addr_t phys_ram_base;
> })
> #define __pa_to_va_nodebug(x) linear_mapping_pa_to_va(x)
>
> +#ifndef CONFIG_DEBUG_VIRTUAL
> #define linear_mapping_va_to_pa(x) ((unsigned long)(x) - kernel_map.va_pa_offset)
> +#else
> +phys_addr_t linear_mapping_va_to_pa(unsigned long x);
> +#endif
> #define kernel_mapping_va_to_pa(y) ({ \
> unsigned long _y = (unsigned long)(y); \
> (IS_ENABLED(CONFIG_XIP_KERNEL) && _y < kernel_map.virt_addr + XIP_OFFSET) ? \
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 478d6763a01a..cc892ba9f787 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -213,6 +213,14 @@ static void __init setup_bootmem(void)
> phys_ram_end = memblock_end_of_DRAM();
> if (!IS_ENABLED(CONFIG_XIP_KERNEL))
> phys_ram_base = memblock_start_of_DRAM();
> +
> + /*
> + * Any use of __va/__pa before this point is wrong as we did not know the
> + * start of DRAM before.
> + */
> + kernel_map.va_pa_offset = PAGE_OFFSET - phys_ram_base;
> + riscv_pfn_base = PFN_DOWN(phys_ram_base);
> +
> /*
> * memblock allocator is not aware of the fact that last 4K bytes of
> * the addressable memory can not be mapped because of IS_ERR_VALUE
> @@ -671,9 +679,16 @@ void __init create_pgd_mapping(pgd_t *pgdp,
>
> static uintptr_t __init best_map_size(phys_addr_t base, phys_addr_t size)
> {
> - /* Upgrade to PMD_SIZE mappings whenever possible */
> - base &= PMD_SIZE - 1;
> - if (!base && size >= PMD_SIZE)
> + if (!(base & (PGDIR_SIZE - 1)) && size >= PGDIR_SIZE)
> + return PGDIR_SIZE;
> +
> + if (!(base & (P4D_SIZE - 1)) && size >= P4D_SIZE)
> + return P4D_SIZE;
> +
> + if (!(base & (PUD_SIZE - 1)) && size >= PUD_SIZE)
> + return PUD_SIZE;
> +
> + if (!(base & (PMD_SIZE - 1)) && size >= PMD_SIZE)
> return PMD_SIZE;
>
> return PAGE_SIZE;
> @@ -982,11 +997,9 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> set_satp_mode();
> #endif
>
> - kernel_map.va_pa_offset = PAGE_OFFSET - kernel_map.phys_addr;
> + kernel_map.va_pa_offset = 0UL;
> kernel_map.va_kernel_pa_offset = kernel_map.virt_addr - kernel_map.phys_addr;
>
> - riscv_pfn_base = PFN_DOWN(kernel_map.phys_addr);
> -
> /*
> * The default maximal physical memory size is KERN_VIRT_SIZE for 32-bit
> * kernel, whereas for 64-bit kernel, the end of the virtual address
> diff --git a/arch/riscv/mm/physaddr.c b/arch/riscv/mm/physaddr.c
> index 9b18bda74154..18706f457da7 100644
> --- a/arch/riscv/mm/physaddr.c
> +++ b/arch/riscv/mm/physaddr.c
> @@ -33,3 +33,19 @@ phys_addr_t __phys_addr_symbol(unsigned long x)
> return __va_to_pa_nodebug(x);
> }
> EXPORT_SYMBOL(__phys_addr_symbol);
> +
> +phys_addr_t linear_mapping_va_to_pa(unsigned long x)
> +{
> + BUG_ON(!kernel_map.va_pa_offset);
> +
> + return ((unsigned long)(x) - kernel_map.va_pa_offset);
> +}
> +EXPORT_SYMBOL(linear_mapping_va_to_pa);
> +
> +void *linear_mapping_pa_to_va(unsigned long x)
> +{
> + BUG_ON(!kernel_map.va_pa_offset);
> +
> + return ((void *)((unsigned long)(x) + kernel_map.va_pa_offset));
> +}
> +EXPORT_SYMBOL(linear_mapping_pa_to_va);
> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index f08b25195ae7..58107bd56f8f 100644
> --- a/drivers/of/fdt.c
> +++ b/drivers/of/fdt.c
> @@ -891,12 +891,13 @@ const void * __init of_flat_dt_match_machine(const void *default_match,
> static void __early_init_dt_declare_initrd(unsigned long start,
> unsigned long end)
> {
> - /* ARM64 would cause a BUG to occur here when CONFIG_DEBUG_VM is
> - * enabled since __va() is called too early. ARM64 does make use
> - * of phys_initrd_start/phys_initrd_size so we can skip this
> - * conversion.
> + /*
> + * __va() is not yet available this early on some platforms. In that
> + * case, the platform uses phys_initrd_start/phys_initrd_size instead
> + * and does the VA conversion itself.
> */
> - if (!IS_ENABLED(CONFIG_ARM64)) {
> + if (!IS_ENABLED(CONFIG_ARM64) &&
> + !(IS_ENABLED(CONFIG_RISCV) && IS_ENABLED(CONFIG_64BIT))) {
There are now two architectures, so maybe it's time for a new config
symbol which would be selected by arm64 and riscv64 and then used here,
e.g.
if (!IS_ENABLED(CONFIG_NO_EARLY_LINEAR_MAP)) {
> initrd_start = (unsigned long)__va(start);
> initrd_end = (unsigned long)__va(end);
> initrd_below_start_ok = 1;
> --
> 2.37.2
>
Otherwise,
Reviewed-by: Andrew Jones <ajones@...tanamicro.com>
Thanks,
drew
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