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Message-ID: <f978c4b9-ef39-4b10-a980-deb23f4c26d3@iscas.ac.cn>
Date: Wed, 31 Jul 2024 11:41:21 +0800
From: Zhe Qiao <qiaozhe@...as.ac.cn>
To: Alexandre Ghiti <alex@...ti.fr>, paul.walmsley@...ive.com,
palmer@...belt.com, aou@...s.berkeley.edu, surenb@...gle.com,
alexghiti@...osinc.com, akpm@...ux-foundation.org,
wangkefeng.wang@...wei.com, willy@...radead.org, qiaozhe@...as.ac.cn
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] riscv/mm: Add handling for VM_FAULT_SIGSEGV in
mm_fault_error()
Hi everyone,
On 2024/7/30 20:43, Alexandre Ghiti wrote:
> Hi Zhe,
>
> On 30/07/2024 09:38, Zhe Qiao wrote:
>> Hello everyone, recently while learning about the Riscv architecture's
>> handling of page fault exceptions in the Linux kernel, I found that
>> there is no handling of VM_CAULT_SIGSEGV in mm_fault_erroneous (), but
>> rather a BUG() is executed directly. Therefore, I simultaneously analyzed
>> the processing procedures of arm64, powerpc, and sh architectures for
>> this area and found that all three architectures have processing for
>> VM_CAULT_SIGSEGV. Therefore, I added relevant processing methods for
>> VM_CAULT_SIGSEGV on the riscv architecture.
>>
>> As a beginner, I am not sure if this processing method is correct and
>> would like to hear the opinions of my seniors.
>
>
> FWIW, we correctly handle "normal" segfaults (ie no VMA or permission access faults).
>
> What we don't handle is handle_mm_fault() returning VM_FAULT_SIGSEGV, which can happen in different situations. For example, the BPF arena stuff implements a vma fault handler which can return VM_FAULT_SIGSEGV (see https://elixir.bootlin.com/linux/v6.10/source/kernel/bpf/arena.c#L273). In that case, we would BUG() instead of correctly killing the process.
>
> So I agree that we need this patch. Can you just rephrase the commit log? I would say something similar (without the link) to what I have just said above. And can you also add the following Fixes tag?
>
> Fixes: 07037db5d479 ("RISC-V: Paging and MMU")
>
> Thanks,
>
> Alex
Thinks for your reply. I have submitted a new patch. Connection address: https://lists.infradead.org/pipermail/linux-riscv/2024-July/058216.html
Thanks,
Zhe
>
>
>>
>> Signed-off-by: Zhe Qiao <qiaozhe@...as.ac.cn>
>> ---
>> arch/riscv/mm/fault.c | 17 +++++++++--------
>> 1 file changed, 9 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
>> index 5224f3733802..868163b904e2 100644
>> --- a/arch/riscv/mm/fault.c
>> +++ b/arch/riscv/mm/fault.c
>> @@ -61,26 +61,27 @@ static inline void no_context(struct pt_regs *regs, unsigned long addr)
>> static inline void mm_fault_error(struct pt_regs *regs, unsigned long addr, vm_fault_t fault)
>> {
>> + if (!user_mode(regs)) {
>> + no_context(regs, addr);
>> + return;
>> + }
>> +
>> if (fault & VM_FAULT_OOM) {
>> /*
>> * We ran out of memory, call the OOM killer, and return the userspace
>> * (which will retry the fault, or kill us if we got oom-killed).
>> */
>> - if (!user_mode(regs)) {
>> - no_context(regs, addr);
>> - return;
>> - }
>> pagefault_out_of_memory();
>> return;
>> } else if (fault & (VM_FAULT_SIGBUS | VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE)) {
>> /* Kernel mode? Handle exceptions or die */
>> - if (!user_mode(regs)) {
>> - no_context(regs, addr);
>> - return;
>> - }
>> do_trap(regs, SIGBUS, BUS_ADRERR, addr);
>> return;
>> + } else if (fault & VM_FAULT_SIGSEGV) {
>> + do_trap(regs, SIGSEGV, SEGV_MAPERR, addr);
>> + return;
>> }
>> +
>> BUG();
>> }
>>
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