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Message-ID: <7fff8202-0be1-4989-959f-8c0b14ca1236@huawei.com>
Date: Tue, 22 Aug 2023 20:12:55 +0800
From: Kefeng Wang <wangkefeng.wang@...wei.com>
To: Christophe Leroy <christophe.leroy@...roup.eu>,
Andrew Morton <akpm@...ux-foundation.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>
CC: "surenb@...gle.com" <surenb@...gle.com>,
"willy@...radead.org" <willy@...radead.org>,
Russell King <linux@...linux.org.uk>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Huacai Chen <chenhuacai@...nel.org>,
WANG Xuerui <kernel@...0n.name>,
Michael Ellerman <mpe@...erman.id.au>,
Nicholas Piggin <npiggin@...il.com>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
Alexander Gordeev <agordeev@...ux.ibm.com>,
Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
Heiko Carstens <hca@...ux.ibm.com>,
Vasily Gorbik <gor@...ux.ibm.com>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Sven Schnelle <svens@...ux.ibm.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Andy Lutomirski <luto@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"x86@...nel.org" <x86@...nel.org>,
"H . Peter Anvin" <hpa@...or.com>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"loongarch@...ts.linux.dev" <loongarch@...ts.linux.dev>,
"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
"linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
"linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>
Subject: Re: [PATCH rfc v2 05/10] powerpc: mm: use try_vma_locked_page_fault()
On 2023/8/22 17:38, Christophe Leroy wrote:
>
>
> Le 21/08/2023 à 14:30, Kefeng Wang a écrit :
>> Use new try_vma_locked_page_fault() helper to simplify code.
>> No functional change intended.
>
> Does it really simplifies code ? It's 32 insertions versus 34 deletions
> so only removing 2 lines.
Yes，it is unfriendly for powerpc as the arch's vma access check is much
complex than other arch,
>
> I don't like the struct vm_fault you are adding because when it was four
> independant variables it was handled through local registers. Now that
> it is a struct it has to go via the stack, leading to unnecessary memory
> read and writes. And going back and forth between architecture code and
> generic code may also be counter-performant.
Because different arch has different var to check vma access, so the
easy way to add them into vmf, I don' find a better way.
>
> Did you make any performance analysis ? Page faults are really a hot
> path when dealling with minor faults.
no, this is only built and rfc to see the feedback about the conversion.
Thanks.
>
> Thanks
> Christophe
>
>>
>> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
>> ---
>> arch/powerpc/mm/fault.c | 66 ++++++++++++++++++++---------------------
>> 1 file changed, 32 insertions(+), 34 deletions(-)
>>
>> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
>> index b1723094d464..52f9546e020e 100644
>> --- a/arch/powerpc/mm/fault.c
>> +++ b/arch/powerpc/mm/fault.c
>> @@ -391,6 +391,22 @@ static int page_fault_is_bad(unsigned long err)
>> #define page_fault_is_bad(__err) ((__err) & DSISR_BAD_FAULT_32S)
>> #endif
>>
>> +#ifdef CONFIG_PER_VMA_LOCK
>> +bool arch_vma_access_error(struct vm_area_struct *vma, struct vm_fault *vmf)
>> +{
>> + int is_exec = TRAP(vmf->regs) == INTERRUPT_INST_STORAGE;
>> + int is_write = page_fault_is_write(vmf->fault_code);
>> +
>> + if (unlikely(access_pkey_error(is_write, is_exec,
>> + (vmf->fault_code & DSISR_KEYFAULT), vma)))
>> + return true;
>> +
>> + if (unlikely(access_error(is_write, is_exec, vma)))
>> + return true;
>> + return false;
>> +}
>> +#endif
>> +
>> /*
>> * For 600- and 800-family processors, the error_code parameter is DSISR
>> * for a data fault, SRR1 for an instruction fault.
>> @@ -407,12 +423,18 @@ static int ___do_page_fault(struct pt_regs *regs, unsigned long address,
>> {
>> struct vm_area_struct * vma;
>> struct mm_struct *mm = current->mm;
>> - unsigned int flags = FAULT_FLAG_DEFAULT;
>> int is_exec = TRAP(regs) == INTERRUPT_INST_STORAGE;
>> int is_user = user_mode(regs);
>> int is_write = page_fault_is_write(error_code);
>> vm_fault_t fault, major = 0;
>> bool kprobe_fault = kprobe_page_fault(regs, 11);
>> + struct vm_fault vmf = {
>> + .real_address = address,
>> + .fault_code = error_code,
>> + .regs = regs,
>> + .flags = FAULT_FLAG_DEFAULT,
>> + };
>> +
>>
>> if (unlikely(debugger_fault_handler(regs) || kprobe_fault))
>> return 0;
>> @@ -463,45 +485,21 @@ static int ___do_page_fault(struct pt_regs *regs, unsigned long address,
>> * mmap_lock held
>> */
>> if (is_user)
>> - flags |= FAULT_FLAG_USER;
>> + vmf.flags |= FAULT_FLAG_USER;
>> if (is_write)
>> - flags |= FAULT_FLAG_WRITE;
>> + vmf.flags |= FAULT_FLAG_WRITE;
>> if (is_exec)
>> - flags |= FAULT_FLAG_INSTRUCTION;
>> + vmf.flags |= FAULT_FLAG_INSTRUCTION;
>>
>> - if (!(flags & FAULT_FLAG_USER))
>> - goto lock_mmap;
>> -
>> - vma = lock_vma_under_rcu(mm, address);
>> - if (!vma)
>> - goto lock_mmap;
>> -
>> - if (unlikely(access_pkey_error(is_write, is_exec,
>> - (error_code & DSISR_KEYFAULT), vma))) {
>> - vma_end_read(vma);
>> - goto lock_mmap;
>> - }
>> -
>> - if (unlikely(access_error(is_write, is_exec, vma))) {
>> - vma_end_read(vma);
>> - goto lock_mmap;
>> - }
>> -
>> - fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, regs);
>> - if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
>> - vma_end_read(vma);
>> -
>> - if (!(fault & VM_FAULT_RETRY)) {
>> - count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
>> + fault = try_vma_locked_page_fault(&vmf);
>> + if (fault == VM_FAULT_NONE)
>> + goto retry;
>> + if (!(fault & VM_FAULT_RETRY))
>> goto done;
>> - }
>> - count_vm_vma_lock_event(VMA_LOCK_RETRY);
>>
>> if (fault_signal_pending(fault, regs))
>> return user_mode(regs) ? 0 : SIGBUS;
>>
>> -lock_mmap:
>> -
>> /* When running in the kernel we expect faults to occur only to
>> * addresses in user space. All other faults represent errors in the
>> * kernel and should generate an OOPS. Unfortunately, in the case of an
>> @@ -528,7 +526,7 @@ static int ___do_page_fault(struct pt_regs *regs, unsigned long address,
>> * make sure we exit gracefully rather than endlessly redo
>> * the fault.
>> */
>> - fault = handle_mm_fault(vma, address, flags, regs);
>> + fault = handle_mm_fault(vma, address, vmf.flags, regs);
>>
>> major |= fault & VM_FAULT_MAJOR;
>>
>> @@ -544,7 +542,7 @@ static int ___do_page_fault(struct pt_regs *regs, unsigned long address,
>> * case.
>> */
>> if (unlikely(fault & VM_FAULT_RETRY)) {
>> - flags |= FAULT_FLAG_TRIED;
>> + vmf.flags |= FAULT_FLAG_TRIED;
>> goto retry;
>> }
>>
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