Re: [PATCH v12 05/11] riscv: mm: avoid enabling interrupts for nofault page faults

[sashiko-bot@kernel.org]

> RISC-V enables interrupts in handle_page_fault() before checking whether
> the fault occurred with fault handling disabled. A nofault access from an
> atomic context can therefore run tracepoints and open an interrupt window
> before reaching the exception-table fixup.
> 
> Handle an exception-table entry before entering the generic fault path when
> fault handling is disabled. Also keep interrupts disabled until such a
> fault has been resolved.
> 
> On 32-bit RISC-V the vmalloc mapping must still be synchronised into the
> current page table before that fixup runs: otherwise a nofault access to a
> not-yet-synced vmalloc address would take the exception-table fixup and
> fail spuriously instead of being resolved. Order the vmalloc
> synchronisation ahead of the nofault fixup. That synchronisation only
> copies an already-established kernel mapping, takes no locks and waits for
> no I/O, so it is safe in the nofault path; if the mapping does not exist it
> falls through to the existing no_context() error handling. This early
> return skips the page-fault tracepoints, as before.
> 
> This makes RISC-V consistent with the expectation that an in-atomic
> nofault access does not enter the normal fault-handling path. It also
> removes one source of re-entry when perf sampling is delivered through an
> SBI Supervisor Software Event (SSE).
> 
> Signed-off-by: Zhanpeng Zhang <zhangzhanpeng.jasper@bytedance.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261029074853.35467-1-zhangzhanpeng.jasper@bytedance.com?part=5