From: Catalin Marinas <catalin.marinas@arm.com>
To: Jia He <justin.he@arm.com>
Cc: "Mark Rutland" <mark.rutland@arm.com>,
"Kaly Xin" <Kaly.Xin@arm.com>,
"Ralph Campbell" <rcampbell@nvidia.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Suzuki Poulose" <Suzuki.Poulose@arm.com>,
"Marc Zyngier" <maz@kernel.org>,
"Anshuman Khandual" <anshuman.khandual@arm.com>,
linux-kernel@vger.kernel.org,
"Matthew Wilcox" <willy@infradead.org>,
linux-mm@kvack.org, "Jérôme Glisse" <jglisse@redhat.com>,
"James Morse" <james.morse@arm.com>,
linux-arm-kernel@lists.infradead.org,
"Punit Agrawal" <punitagrawal@gmail.com>,
hejianet@gmail.com, "Thomas Gleixner" <tglx@linutronix.de>,
nd@arm.com, "Will Deacon" <will@kernel.org>,
"Alex Van Brunt" <avanbrunt@nvidia.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
"Robin Murphy" <robin.murphy@arm.com>
Subject: Re: [PATCH v8 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared
Date: Mon, 23 Sep 2019 18:04:34 +0100 [thread overview]
Message-ID: <20190923170433.GE10192@arrakis.emea.arm.com> (raw)
In-Reply-To: <20190921135054.142360-4-justin.he@arm.com>
On Sat, Sep 21, 2019 at 09:50:54PM +0800, Jia He wrote:
> @@ -2151,21 +2163,53 @@ static inline void cow_user_page(struct page *dst, struct page *src, unsigned lo
> * fails, we just zero-fill it. Live with it.
> */
> if (unlikely(!src)) {
> - void *kaddr = kmap_atomic(dst);
> - void __user *uaddr = (void __user *)(va & PAGE_MASK);
> + void *kaddr;
> + pte_t entry;
> + void __user *uaddr = (void __user *)(addr & PAGE_MASK);
>
> + /* On architectures with software "accessed" bits, we would
> + * take a double page fault, so mark it accessed here.
> + */
Nitpick: please follow the kernel coding style for multi-line comments
(above and the for the rest of the patch):
/*
* Your multi-line comment.
*/
> + if (arch_faults_on_old_pte() && !pte_young(vmf->orig_pte)) {
> + vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr,
> + &vmf->ptl);
> + if (likely(pte_same(*vmf->pte, vmf->orig_pte))) {
> + entry = pte_mkyoung(vmf->orig_pte);
> + if (ptep_set_access_flags(vma, addr,
> + vmf->pte, entry, 0))
> + update_mmu_cache(vma, addr, vmf->pte);
> + } else {
> + /* Other thread has already handled the fault
> + * and we don't need to do anything. If it's
> + * not the case, the fault will be triggered
> + * again on the same address.
> + */
> + pte_unmap_unlock(vmf->pte, vmf->ptl);
> + return false;
> + }
> + pte_unmap_unlock(vmf->pte, vmf->ptl);
> + }
Another nit, you could rewrite this block slightly to avoid too much
indentation. Something like (untested):
if (arch_faults_on_old_pte() && !pte_young(vmf->orig_pte)) {
vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr,
&vmf->ptl);
if (unlikely(!pte_same(*vmf->pte, vmf->orig_pte))) {
/*
* Other thread has already handled the fault
* and we don't need to do anything. If it's
* not the case, the fault will be triggered
* again on the same address.
*/
pte_unmap_unlock(vmf->pte, vmf->ptl);
return false;
}
entry = pte_mkyoung(vmf->orig_pte);
if (ptep_set_access_flags(vma, addr,
vmf->pte, entry, 0))
update_mmu_cache(vma, addr, vmf->pte);
pte_unmap_unlock(vmf->pte, vmf->ptl);
}
> +
> + kaddr = kmap_atomic(dst);
Since you moved the kmap_atomic() here, could the above
arch_faults_on_old_pte() run in a preemptible context? I suggested to
add a WARN_ON in patch 2 to be sure.
> /*
> * This really shouldn't fail, because the page is there
> * in the page tables. But it might just be unreadable,
> * in which case we just give up and fill the result with
> * zeroes.
> */
> - if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE))
> + if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) {
> + /* Give a warn in case there can be some obscure
> + * use-case
> + */
> + WARN_ON_ONCE(1);
That's more of a question for the mm guys: at this point we do the
copying with the ptl released; is there anything else that could have
made the pte old in the meantime? I think unuse_pte() is only called on
anonymous vmas, so it shouldn't be the case here.
> clear_page(kaddr);
> + }
> kunmap_atomic(kaddr);
> flush_dcache_page(dst);
> } else
> - copy_user_highpage(dst, src, va, vma);
> + copy_user_highpage(dst, src, addr, vma);
> +
> + return true;
> }
--
Catalin
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next prev parent reply other threads:[~2019-09-23 17:04 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-21 13:50 [PATCH v8 0/3] fix double page fault on arm64 Jia He
2019-09-21 13:50 ` [PATCH v8 1/3] arm64: cpufeature: introduce helper cpu_has_hw_af() Jia He
2019-09-23 16:07 ` Catalin Marinas
2019-09-24 1:50 ` Justin He (Arm Technology China)
2019-09-21 13:50 ` [PATCH v8 2/3] arm64: mm: implement arch_faults_on_old_pte() on arm64 Jia He
2019-09-23 16:18 ` Catalin Marinas
2019-09-24 2:17 ` Justin He (Arm Technology China)
2019-09-21 13:50 ` [PATCH v8 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared Jia He
2019-09-21 15:31 ` Matthew Wilcox
2019-09-23 8:28 ` Kirill A. Shutemov
2019-09-23 17:04 ` Catalin Marinas [this message]
2019-09-24 6:43 ` Justin He (Arm Technology China)
2019-09-24 10:33 ` Catalin Marinas
2019-09-24 11:59 ` Kirill A. Shutemov
2019-09-24 15:29 ` Jia He
2019-09-24 16:35 ` Catalin Marinas
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