Messages in this thread | | | From | Sami Tolvanen <> | Date | Mon, 24 Jul 2023 09:34:04 -0700 | Subject | Re: [PATCH v2] riscv: VMAP_STACK overflow detection thread-safe |
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On Thu, Jul 20, 2023 at 8:06 AM Guo Ren <guoren@kernel.org> wrote: > > On Thu, Jul 20, 2023 at 8:19 AM Sami Tolvanen <samitolvanen@google.com> wrote: > > > > Are you planning on resending this patch? I see it didn't gain much > > traction last time, but this looks like a much cleaner solution for > > selecting the overflow stack than having a `shadow_stack` and calling > > to C to compute the per-CPU offset. The asm_per_cpu macro also would > > come in handy when implementing CONFIG_SHADOW_CALL_STACK, which we'd > > like to have on RISC-V too. > I remember we ended up with an atomic lock mechanism instead of percpu > offset, so what's the benefit of percpu style in overflow_stack path?
The benefit is not needing a separate temporary stack and locks just to compute the per-CPU offset. With CONFIG_SHADOW_CALL_STACK, we would also need a "shadow" shadow call stack in this case before calling to C code, at which point computing the offsets directly in assembly is just significantly cleaner and without concurrency issues.
Sami
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