From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
David Hildenbrand <david@redhat.com>,
catalin.marinas@arm.com, linux-kernel@vger.kernel.org,
Steven Price <steven.price@arm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Robin Murphy <robin.murphy@arm.com>,
Ard Biesheuvel <ardb@kernel.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] arm64/mm: Validate hotplug range before creating linear mapping
Date: Tue, 29 Sep 2020 13:34:24 +0530 [thread overview]
Message-ID: <09266aed-7eef-5b16-5d52-0dcb7dcb7246@arm.com> (raw)
In-Reply-To: <20200928203539.GA12218@willie-the-truck>
On 09/29/2020 02:05 AM, Will Deacon wrote:
> On Thu, Sep 17, 2020 at 02:16:42PM +0530, 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)));
>> +}
>
> Why isn't this implemented using the existing __is_lm_address()?
Not sure, if I understood your suggestion here. The physical address range
[start..start + size] needs to be checked against maximum physical range
that can be represented inside effective boundaries for the linear mapping
i.e [__pa(_PAGE_OFFSET(vabits_actual)..__pa(PAGE_END - 1)].
Are you suggesting [start..start + size] should be first be converted into
a virtual address range and then checked against __is_lm_addresses() ? But
is not deriving the physical range from from know limits of linear mapping
much cleaner ?
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next prev parent reply other threads:[~2020-09-29 8:06 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-17 8:46 [PATCH] arm64/mm: Validate hotplug range before creating linear mapping Anshuman Khandual
2020-09-28 20:35 ` Will Deacon
2020-09-29 8:04 ` Anshuman Khandual [this message]
2020-09-29 15:22 ` Will Deacon
2020-09-30 8:02 ` Anshuman Khandual
2020-09-30 11:01 ` Ard Biesheuvel
2020-10-06 6:28 ` Anshuman Khandual
2020-10-06 6:35 ` Anshuman Khandual
2020-10-12 7:29 ` Ard Biesheuvel
2020-10-14 5:06 ` Anshuman Khandual
2020-10-14 6:37 ` Ard Biesheuvel
2020-10-06 15:34 ` David Hildenbrand
2020-10-07 2:50 ` Anshuman Khandual
2020-10-07 8:39 ` David Hildenbrand
2020-10-19 11:23 ` Anshuman Khandual
2020-10-19 14:58 ` David Hildenbrand
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