From: Jia He <hejianet@gmail.com>
To: Matthew Wilcox <willy@infradead.org>, 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>,
"Catalin Marinas" <catalin.marinas@arm.com>,
"Anshuman Khandual" <anshuman.khandual@arm.com>,
linux-kernel@vger.kernel.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>,
"Marc Zyngier" <maz@kernel.org>,
"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 v7 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared
Date: Sat, 21 Sep 2019 21:19:34 +0800 [thread overview]
Message-ID: <dbfc9da4-6650-5c9e-59c6-16e0f234b9c8@gmail.com> (raw)
In-Reply-To: <20190920155300.GC15392@bombadil.infradead.org>
[On behalf of justin.he@arm.com]
Hi Matthew
On 2019/9/20 23:53, Matthew Wilcox wrote:
> On Fri, Sep 20, 2019 at 09:54:37PM +0800, Jia He wrote:
>> -static inline void cow_user_page(struct page *dst, struct page *src, unsigned long va, struct vm_area_struct *vma)
>> +static inline int cow_user_page(struct page *dst, struct page *src,
>> + struct vm_fault *vmf)
>> {
> Can we talk about the return type here?
>
>> + } 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 -1;
> ...
>> + return 0;
>> }
> So -1 for "try again" and 0 for "succeeded".
>
>> + if (cow_user_page(new_page, old_page, vmf)) {
> Then we use it like a bool. But it's kind of backwards from a bool because
> false is success.
>
>> + /* COW failed, if the fault was solved by other,
>> + * it's fine. If not, userspace would re-fault on
>> + * the same address and we will handle the fault
>> + * from the second attempt.
>> + */
>> + put_page(new_page);
>> + if (old_page)
>> + put_page(old_page);
>> + return 0;
> And we don't use the return value; in fact we invert it.
>
> Would this make more sense:
>
> static inline bool cow_user_page(struct page *dst, struct page *src,
> struct vm_fault *vmf)
> ...
> pte_unmap_unlock(vmf->pte, vmf->ptl);
> return false;
> ...
> return true;
> ...
> if (!cow_user_page(new_page, old_page, vmf)) {
>
> That reads more sensibly for me. We could also go with returning a
> vm_fault_t, but that would be more complex than needed today, I think.
Ok, will change the return type to bool as you suggested.
Thanks
---
Cheers,
Justin (Jia He)
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prev parent reply other threads:[~2019-09-21 13:20 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-20 13:54 [PATCH v7 0/3] fix double page fault on arm64 Jia He
2019-09-20 13:54 ` [PATCH v7 1/3] arm64: cpufeature: introduce helper cpu_has_hw_af() Jia He
2019-09-20 13:54 ` [PATCH v7 2/3] arm64: mm: implement arch_faults_on_old_pte() on arm64 Jia He
2019-09-20 13:54 ` [PATCH v7 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared Jia He
2019-09-20 14:21 ` Kirill A. Shutemov
2019-09-20 14:24 ` Justin He (Arm Technology China)
2019-09-20 15:53 ` Matthew Wilcox
2019-09-20 17:00 ` Kirill A. Shutemov
2019-09-21 13:19 ` Jia He [this message]
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