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Message-ID: <99beed41-c7b1-3d62-9c6f-1b9999a3fefe@amd.com>
Date: Wed, 9 Oct 2024 07:26:11 +0200
From: "Gupta, Pankaj" <pankaj.gupta@....com>
To: John Hubbard <jhubbard@...dia.com>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: Thomas Gleixner <tglx@...utronix.de>, David Hildenbrand
<david@...hat.com>, Will Deacon <will@...nel.org>,
Alistair Popple <apopple@...dia.com>, Jordan Niethe <jniethe@...dia.com>,
linux-arm-kernel@...ts.infradead.org, x86@...nel.org, linux-mm@...ck.org,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kaslr: rename physmem_end and PHYSMEM_END to
direct_map_physmem_end
On 10/9/2024 4:50 AM, John Hubbard wrote:
> For clarity. It's increasingly hard to reason about the code, when KASLR
> is moving around the boundaries. In this case where KASLR is randomizing
> the location of the kernel image within physical memory, the maximum
> number of address bits for physical memory has not changed.
>
> What has changed is the ending address of memory that is allowed to be
> directly mapped by the kernel.
>
> Let's name the variable, and the associated macro accordingly.
>
> Also, enhance the comment above the direct_map_physmem_end definition,
> to further clarify how this all works.
>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Alistair Popple <apopple@...dia.com>
> Cc: Jordan Niethe <jniethe@...dia.com>
> Cc: David Hildenbrand <david@...hat.com>
> Signed-off-by: John Hubbard <jhubbard@...dia.com>
Seems reasonable to me.
Reviewed-by: Pankaj Gupta <pankaj.gupta@....com>
> ---
>
> David Hildenbrand, I recall you had an unanswered question in this
> vicinity [1] when tglx's recent kaslr fix was being reviewed. Maybe this
> will help with that.
>
>
> [1] https://lore.kernel.org/linux-mm/ee205448-5fdd-495e-9d7c-c8a2b59f9c9e@roeck-us.net/T/#mdf442f077c9023590e144dbed2b04a109793484d
>
> thanks,
> John Hubbard
>
>
> arch/arm64/include/asm/memory.h | 2 +-
> arch/x86/include/asm/page_64.h | 2 +-
> arch/x86/include/asm/pgtable_64_types.h | 2 +-
> arch/x86/mm/init_64.c | 2 +-
> arch/x86/mm/kaslr.c | 14 +++++++++-----
> include/linux/mm.h | 6 +++---
> kernel/resource.c | 4 ++--
> mm/memory_hotplug.c | 2 +-
> mm/sparse.c | 2 +-
> 9 files changed, 20 insertions(+), 16 deletions(-)
>
> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> index 0480c61dbb4f..73eaa8c2536a 100644
> --- a/arch/arm64/include/asm/memory.h
> +++ b/arch/arm64/include/asm/memory.h
> @@ -110,7 +110,7 @@
> #define PAGE_END (_PAGE_END(VA_BITS_MIN))
> #endif /* CONFIG_KASAN */
>
> -#define PHYSMEM_END __pa(PAGE_END - 1)
> +#define DIRECT_MAP_PHYSMEM_END __pa(PAGE_END - 1)
>
> #define MIN_THREAD_SHIFT (14 + KASAN_THREAD_SHIFT)
>
> diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
> index f3d257c45225..d63576608ce7 100644
> --- a/arch/x86/include/asm/page_64.h
> +++ b/arch/x86/include/asm/page_64.h
> @@ -17,7 +17,7 @@ extern unsigned long phys_base;
> extern unsigned long page_offset_base;
> extern unsigned long vmalloc_base;
> extern unsigned long vmemmap_base;
> -extern unsigned long physmem_end;
> +extern unsigned long direct_map_physmem_end;
>
> static __always_inline unsigned long __phys_addr_nodebug(unsigned long x)
> {
> diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
> index a98e53491a4e..ec68f8369bdc 100644
> --- a/arch/x86/include/asm/pgtable_64_types.h
> +++ b/arch/x86/include/asm/pgtable_64_types.h
> @@ -141,7 +141,7 @@ extern unsigned int ptrs_per_p4d;
> #endif /* CONFIG_DYNAMIC_MEMORY_LAYOUT */
>
> #ifdef CONFIG_RANDOMIZE_MEMORY
> -# define PHYSMEM_END physmem_end
> +# define DIRECT_MAP_PHYSMEM_END direct_map_physmem_end
> #endif
>
> /*
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index ff253648706f..5a564130b9d0 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -961,7 +961,7 @@ int add_pages(int nid, unsigned long start_pfn, unsigned long nr_pages,
> unsigned long end = ((start_pfn + nr_pages) << PAGE_SHIFT) - 1;
> int ret;
>
> - if (WARN_ON_ONCE(end > PHYSMEM_END))
> + if (WARN_ON_ONCE(end > DIRECT_MAP_PHYSMEM_END))
> return -ERANGE;
>
> ret = __add_pages(nid, start_pfn, nr_pages, params);
> diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
> index 230f1dee4f09..70d3353c92fa 100644
> --- a/arch/x86/mm/kaslr.c
> +++ b/arch/x86/mm/kaslr.c
> @@ -52,7 +52,7 @@ static __initdata struct kaslr_memory_region {
> } kaslr_regions[] = {
> {
> .base = &page_offset_base,
> - .end = &physmem_end,
> + .end = &direct_map_physmem_end,
> },
> {
> .base = &vmalloc_base,
> @@ -62,8 +62,12 @@ static __initdata struct kaslr_memory_region {
> },
> };
>
> -/* The end of the possible address space for physical memory */
> -unsigned long physmem_end __ro_after_init;
> +/*
> + * The end of the physical address space that can be mapped directly by the
> + * kernel. This starts out at (1<<MAX_PHYSMEM_BITS) - 1), but KASLR may reduce
> + * that in order to increase the available entropy for mapping other regions.
> + */
> +unsigned long direct_map_physmem_end __ro_after_init;
>
> /* Get size in bytes used by the memory region */
> static inline unsigned long get_padding(struct kaslr_memory_region *region)
> @@ -94,7 +98,7 @@ void __init kernel_randomize_memory(void)
> BUILD_BUG_ON(vaddr_end > __START_KERNEL_map);
>
> /* Preset the end of the possible address space for physical memory */
> - physmem_end = ((1ULL << MAX_PHYSMEM_BITS) - 1);
> + direct_map_physmem_end = ((1ULL << MAX_PHYSMEM_BITS) - 1);
> if (!kaslr_memory_enabled())
> return;
>
> @@ -145,7 +149,7 @@ void __init kernel_randomize_memory(void)
> vaddr += get_padding(&kaslr_regions[i]);
> /*
> * KASLR trims the maximum possible size of the
> - * direct-map. Update the physmem_end boundary.
> + * direct-map. Update the direct_map_physmem_end boundary.
> * No rounding required as the region starts
> * PUD aligned and size is in units of TB.
> */
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index ecf63d2b0582..92c35fb60d18 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -97,11 +97,11 @@ extern const int mmap_rnd_compat_bits_max;
> extern int mmap_rnd_compat_bits __read_mostly;
> #endif
>
> -#ifndef PHYSMEM_END
> +#ifndef DIRECT_MAP_PHYSMEM_END
> # ifdef MAX_PHYSMEM_BITS
> -# define PHYSMEM_END ((1ULL << MAX_PHYSMEM_BITS) - 1)
> +# define DIRECT_MAP_PHYSMEM_END ((1ULL << MAX_PHYSMEM_BITS) - 1)
> # else
> -# define PHYSMEM_END (((phys_addr_t)-1)&~(1ULL<<63))
> +# define DIRECT_MAP_PHYSMEM_END (((phys_addr_t)-1)&~(1ULL<<63))
> # endif
> #endif
>
> diff --git a/kernel/resource.c b/kernel/resource.c
> index b730bd28b422..afa3ad09b834 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -1871,7 +1871,7 @@ static resource_size_t gfr_start(struct resource *base, resource_size_t size,
> if (flags & GFR_DESCENDING) {
> resource_size_t end;
>
> - end = min_t(resource_size_t, base->end, PHYSMEM_END);
> + end = min_t(resource_size_t, base->end, DIRECT_MAP_PHYSMEM_END);
> return end - size + 1;
> }
>
> @@ -1888,7 +1888,7 @@ static bool gfr_continue(struct resource *base, resource_size_t addr,
> * @size did not wrap 0.
> */
> return addr > addr - size &&
> - addr <= min_t(resource_size_t, base->end, PHYSMEM_END);
> + addr <= min_t(resource_size_t, base->end, DIRECT_MAP_PHYSMEM_END);
> }
>
> static resource_size_t gfr_next(resource_size_t addr, resource_size_t size,
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 621ae1015106..c43b4e7fb298 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1681,7 +1681,7 @@ struct range __weak arch_get_mappable_range(void)
>
> struct range mhp_get_pluggable_range(bool need_mapping)
> {
> - const u64 max_phys = PHYSMEM_END;
> + const u64 max_phys = DIRECT_MAP_PHYSMEM_END;
> struct range mhp_range;
>
> if (need_mapping) {
> diff --git a/mm/sparse.c b/mm/sparse.c
> index dc38539f8560..4cb9793f0b52 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -129,7 +129,7 @@ static inline int sparse_early_nid(struct mem_section *section)
> static void __meminit mminit_validate_memmodel_limits(unsigned long *start_pfn,
> unsigned long *end_pfn)
> {
> - unsigned long max_sparsemem_pfn = (PHYSMEM_END + 1) >> PAGE_SHIFT;
> + unsigned long max_sparsemem_pfn = (DIRECT_MAP_PHYSMEM_END + 1) >> PAGE_SHIFT;
>
> /*
> * Sanity checks - do not allow an architecture to pass
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