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Message-ID: <CAJF2gTRFvSvEvQeDugdp73o7w4ArdtQ99JScEbLkaLnFcftVcA@mail.gmail.com> Date: Thu, 20 Jul 2023 23:06:12 +0800 From: Guo Ren <guoren@...nel.org> To: Sami Tolvanen <samitolvanen@...gle.com> Cc: Deepak Gupta <debug@...osinc.com>, palmer@...belt.com, linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org, Jisheng Zhang <jszhang@...nel.org> Subject: Re: [PATCH v2] riscv: VMAP_STACK overflow detection thread-safe On Thu, Jul 20, 2023 at 8:19 AM Sami Tolvanen <samitolvanen@...gle.com> wrote: > > Hi Deepak, > > On Thu, Nov 24, 2022 at 01:48:45AM -0800, Deepak Gupta wrote: > > commit 31da94c25aea ("riscv: add VMAP_STACK overflow detection") added > > support for CONFIG_VMAP_STACK. If overflow is detected, CPU switches to > > `shadow_stack` temporarily before switching finally to per-cpu > > `overflow_stack`. > > > > If two CPUs/harts are racing and end up in over flowing kernel stack, one > > or both will end up corrupting each other state because `shadow_stack` is > > not per-cpu. This patch optimizes per-cpu overflow stack switch by > > directly picking per-cpu `overflow_stack` and gets rid of `shadow_stack`. > > 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? > > Sami -- Best Regards Guo Ren
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