Messages in this thread | | | Subject | Re: [PATCH V2] arm64/mm: Intercept pfn changes in set_pte_at() | From | Muchun Song <> | Date | Thu, 2 Feb 2023 17:51:39 +0800 |
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> On Feb 1, 2023, at 20:20, Catalin Marinas <catalin.marinas@arm.com> wrote: > > On Tue, Jan 31, 2023 at 03:49:51PM +0000, Will Deacon wrote: >> On Fri, Jan 27, 2023 at 12:43:17PM +0000, Robin Murphy wrote: >>> On 2023-01-26 13:33, Will Deacon wrote: >>>> On Tue, Jan 24, 2023 at 11:11:49AM +0530, Anshuman Khandual wrote: >>>>> On 1/9/23 10:58, Anshuman Khandual wrote: >>>>>> Changing pfn on a user page table mapped entry, without first going through >>>>>> break-before-make (BBM) procedure is unsafe. This just updates set_pte_at() >>>>>> to intercept such changes, via an updated pgattr_change_is_safe(). This new >>>>>> check happens via __check_racy_pte_update(), which has now been renamed as >>>>>> __check_safe_pte_update(). >>>>>> >>>>>> Cc: Catalin Marinas <catalin.marinas@arm.com> >>>>>> Cc: Will Deacon <will@kernel.org> >>>>>> Cc: Mark Rutland <mark.rutland@arm.com> >>>>>> Cc: Andrew Morton <akpm@linux-foundation.org> >>>>>> Cc: linux-arm-kernel@lists.infradead.org >>>>>> Cc: linux-kernel@vger.kernel.org >>>>>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> >>>>>> --- >>>>>> This applies on v6.2-rc3. This patch had some test time on an internal CI >>>>>> system without any issues being reported. >>>>> >>>>> Gentle ping, any updates on this patch ? Still any concerns ? >>>> >>>> I don't think we really got to the bottom of Mark's concerns with >>>> unreachable ptes on the stack, did we? I also have vague recollections >>>> of somebody (Robin?) running into issues with the vmap code not honouring >>>> BBM. >>> >>> Doesn't ring a bell, so either it wasn't me, or it was many years ago and >>> about 5 levels deep into trying to fix something else :/ >> >> Bah, sorry! Catalin reckons it may have been him talking about the vmemmap. > > Indeed. The discussion with Anshuman started from this thread: > > https://lore.kernel.org/all/20221025014215.3466904-1-mawupeng1@huawei.com/ > > We already trip over the existing checks even without Anshuman's patch, > though only by chance. We are not setting the software PTE_DIRTY on the > new pte (we don't bother with this bit for kernel mappings). > > Given that the vmemmap ptes are still live when such change happens and > no-one came with a solution to the break-before-make problem, I propose > we revert the arm64 part of commit 47010c040dec ("mm: hugetlb_vmemmap: > cleanup CONFIG_HUGETLB_PAGE_FREE_VMEMMAP*"). We just need this hunk: > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 27b2592698b0..5263454a5794 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -100,7 +100,6 @@ config ARM64 > select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT > select ARCH_WANT_FRAME_POINTERS > select ARCH_WANT_HUGE_PMD_SHARE if ARM64_4K_PAGES || (ARM64_16K_PAGES && !ARM64_VA_BITS_36) > - select ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
Maybe it is a little overkill for HVO as it can significantly minimize the overhead of vmemmap on ARM64 servers for some workloads (like qemu, DPDK). So I don't think disabling it is a good approach. Indeed, HVO broke BBM, but the waring does not affect anything since the tail vmemmap pages are supposed to be read-only. So, I suggest skipping warnings if it is the vmemmap address in set_pte_at(). What do you think of?
Muchun, Thanks.
> select ARCH_WANT_LD_ORPHAN_WARN > select ARCH_WANTS_NO_INSTR > select ARCH_WANTS_THP_SWAP if ARM64_4K_PAGES > > -- > Catalin
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