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Message-ID: <20230125114229.hrhsyw4aegrnmoau@orel>
Date: Wed, 25 Jan 2023 12:42:29 +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>,
Conor Dooley <conor@...nel.org>,
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 v5 2/2] riscv: Use PUD/P4D/PGD pages for the linear
mapping
On Wed, Jan 25, 2023 at 09:12:14AM +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.
>
> Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
> Acked-by: Rob Herring <robh@...nel.org> # DT bits
> Reviewed-by: Andrew Jones <ajones@...tanamicro.com>
> ---
> arch/riscv/include/asm/page.h | 16 ++++++++++++++++
> arch/riscv/mm/init.c | 24 ++++++++++++++++++------
> arch/riscv/mm/physaddr.c | 16 ++++++++++++++++
> drivers/of/fdt.c | 11 ++++++-----
> 4 files changed, 56 insertions(+), 11 deletions(-)
>
> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> index 728eee53152a..bd7b9dda1e4f 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
> #define ARCH_PFN_OFFSET (PFN_DOWN(phys_ram_base))
> #else
> @@ -121,7 +129,11 @@ 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) ? \
> @@ -130,7 +142,11 @@ 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 225a7d2b65cc..9dfc0afdb114 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -213,6 +213,13 @@ 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;
> +
> /*
> * 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
> @@ -667,9 +674,16 @@ 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;
> @@ -978,11 +992,9 @@ 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;
>
> - phys_ram_base = 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));
I missed pointing out this superfluous () in this function and the one
above it in my first review, but it's just a nit anyway.
Thanks,
drew
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