Messages in this thread | | | Subject | Re: [PATCH] arm64/mm: Validate hotplug range before creating linear mapping | From | Anshuman Khandual <> | Date | Wed, 7 Oct 2020 08:20:14 +0530 |
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On 10/06/2020 09:04 PM, David Hildenbrand wrote: > On 17.09.20 10:46, Anshuman Khandual wrote: >> During memory hotplug process, the linear mapping should not be created for >> a given memory range if that would fall outside the maximum allowed linear >> range. Else it might cause memory corruption in the kernel virtual space. >> >> Maximum linear mapping region is [PAGE_OFFSET..(PAGE_END -1)] accommodating >> both its ends but excluding PAGE_END. Max physical range that can be mapped >> inside this linear mapping range, must also be derived from its end points. >> >> When CONFIG_ARM64_VA_BITS_52 is enabled, PAGE_OFFSET is computed with the >> assumption of 52 bits virtual address space. However, if the CPU does not >> support 52 bits, then it falls back using 48 bits instead and the PAGE_END >> is updated to reflect this using the vabits_actual. As for PAGE_OFFSET, >> bits [51..48] are ignored by the MMU and remain unchanged, even though the >> effective start address of linear map is now slightly different. Hence, to >> reliably check the physical address range mapped by the linear map, the >> start address should be calculated using vabits_actual. This ensures that >> arch_add_memory() validates memory hot add range for its potential linear >> mapping requirement, before creating it with __create_pgd_mapping(). >> >> Cc: Catalin Marinas <catalin.marinas@arm.com> >> Cc: Will Deacon <will@kernel.org> >> Cc: Mark Rutland <mark.rutland@arm.com> >> Cc: Ard Biesheuvel <ardb@kernel.org> >> Cc: Steven Price <steven.price@arm.com> >> Cc: Robin Murphy <robin.murphy@arm.com> >> Cc: David Hildenbrand <david@redhat.com> >> Cc: Andrew Morton <akpm@linux-foundation.org> >> Cc: linux-arm-kernel@lists.infradead.org >> Cc: linux-kernel@vger.kernel.org >> Fixes: 4ab215061554 ("arm64: Add memory hotplug support") >> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> >> --- >> arch/arm64/mm/mmu.c | 27 +++++++++++++++++++++++++++ >> 1 file changed, 27 insertions(+) >> >> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c >> index 75df62fea1b6..d59ffabb9c84 100644 >> --- a/arch/arm64/mm/mmu.c >> +++ b/arch/arm64/mm/mmu.c >> @@ -1433,11 +1433,38 @@ static void __remove_pgd_mapping(pgd_t *pgdir, unsigned long start, u64 size) >> free_empty_tables(start, end, PAGE_OFFSET, PAGE_END); >> } >> >> +static bool inside_linear_region(u64 start, u64 size) >> +{ >> + /* >> + * Linear mapping region is the range [PAGE_OFFSET..(PAGE_END - 1)] >> + * accommodating both its ends but excluding PAGE_END. Max physical >> + * range which can be mapped inside this linear mapping range, must >> + * also be derived from its end points. >> + * >> + * With CONFIG_ARM64_VA_BITS_52 enabled, PAGE_OFFSET is defined with >> + * the assumption of 52 bits virtual address space. However, if the >> + * CPU does not support 52 bits, it falls back using 48 bits and the >> + * PAGE_END is updated to reflect this using the vabits_actual. As >> + * for PAGE_OFFSET, bits [51..48] are ignored by the MMU and remain >> + * unchanged, even though the effective start address of linear map >> + * is now slightly different. Hence, to reliably check the physical >> + * address range mapped by the linear map, the start address should >> + * be calculated using vabits_actual. >> + */ >> + return ((start >= __pa(_PAGE_OFFSET(vabits_actual))) >> + && ((start + size) <= __pa(PAGE_END - 1))); >> +} >> + >> int arch_add_memory(int nid, u64 start, u64 size, >> struct mhp_params *params) >> { >> int ret, flags = 0; >> >> + if (!inside_linear_region(start, size)) { >> + pr_err("[%llx %llx] is outside linear mapping region\n", start, start + size); >> + return -EINVAL; >> + } >> + >> if (rodata_full || debug_pagealloc_enabled()) >> flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS; >> >> > > Can we please provide a generic way to figure limits like that out, > especially, before calling add_memory() and friends? > > We do have __add_pages()->check_hotplug_memory_addressable() where we > already check against MAX_PHYSMEM_BITS.
Initially, I thought about check_hotplug_memory_addressable() but the existing check that asserts end of hotplug wrt MAX_PHYSMEM_BITS, is generic in nature. AFAIK the linear mapping problem is arm64 specific, hence I was not sure whether to add an arch specific callback which will give platform an opportunity to weigh in for these ranges.
But hold on, check_hotplug_memory_addressable() only gets called from __add_pages() after linear mapping creation in arch_add_memory(). How would it help ? We need some thing for add_memory(), its variants and also possibly for memremap_pages() when it calls arch_add_memory().
> > What I'd prefer is a way to get > > 1. Lower address limit we can use for add_memory() and friends > 2. Upper address limit we can use for add_memory() and friends
A structure based range.
> > something like > > > struct range memhp_get_addressable_range(void) > { > const u64 max_phys = (1ull << (MAX_PHYSMEM_BITS + 1)) - 1; > struct range range = arch_get_mappable_range();
What would you suggest as the default fallback range if a platform does not define this callback.
> > if (range.start > max_phys) { > range.start = 0; > range.end = 0; > } > range.end = max_t(u64, range.end, max_phys);
min_t instead ?
> > return range; > } > > > That, we can use in check_hotplug_memory_addressable(), and also allow > add_memory*() users to make use of it.
So this check would happen twice during a hotplug ?
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