From: Kyle Huey <me@kylehuey.com> To: open list <linux-kernel@vger.kernel.org> Cc: "moderated list:ARM PORT" <linux-arm-kernel@lists.infradead.org>, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>, yyc1992@gmail.com, Keno Fischer <keno@juliacomputing.com>, "Robert O'Callahan" <robert@ocallahan.org>, Thomas Gleixner <tglx@linutronix.de>, Borislav Petkov <bp@alien8.de>, Marc Zyngier <maz@kernel.org>, Suzuki K Poulose <suzuki.poulose@arm.com>, Will Deacon <will.deacon@arm.com> Subject: arm64 equivalents of PR_SET_TSC/ARCH_SET_CPUID Date: Sat, 21 May 2022 13:07:14 -0700 [thread overview] Message-ID: <CAP045ApiMSvP--f2E0=VdMbjE8oibvy921m8JASf4kaCCuU2RA@mail.gmail.com> (raw) There is ongoing work by Yichao Yu to make rr, a userspace record and replay debugger[0], production quality on arm64[1]. One of the bigger remaining issues is the kernel's emulation of accesses to certain system registers[2] that reflect timing and CPU capabilities and are either non-deterministic or can vary from processor to processor. We would like to add the ability to tell the kernel to decline to emulate these instructions for a given task and pass that responsibility onto the supervising rr ptracer. There are analogous processor features and disabling mechanisms on x86. The RDTSC instruction is controlled by prctl(PR_SET_TSC) and the CPUID instruction is controlled (when the hardware allows) by arch_prctl(ARCH_SET_CPUID). The questions I'd like to raise are: 1. Is it appropriate to reuse PR_SET_TSC for roughly equivalent functionality on AArch64? (even if the AArch64 feature is not actually named Time Stamp Counter). 2. Likewise for ARCH_SET_CPUID 3. Since arch_prctl is x86-only, does it make more sense to add arch_prctl to arm64 or to duplicate ARCH_SET_CPUID into the prctl world? (e.g. a PR_SET_CPUID that works on both x86/arm64) - Kyle [0] https://rr-project.org/ [1] https://github.com/rr-debugger/rr/issues/3234 [2] e.g. CNTVCT_EL0 and MIDR_EL1, among others
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From: Kyle Huey <me@kylehuey.com> To: open list <linux-kernel@vger.kernel.org> Cc: "moderated list:ARM PORT" <linux-arm-kernel@lists.infradead.org>, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>, yyc1992@gmail.com, Keno Fischer <keno@juliacomputing.com>, "Robert O'Callahan" <robert@ocallahan.org>, Thomas Gleixner <tglx@linutronix.de>, Borislav Petkov <bp@alien8.de>, Marc Zyngier <maz@kernel.org>, Suzuki K Poulose <suzuki.poulose@arm.com>, Will Deacon <will.deacon@arm.com> Subject: arm64 equivalents of PR_SET_TSC/ARCH_SET_CPUID Date: Sat, 21 May 2022 13:07:14 -0700 [thread overview] Message-ID: <CAP045ApiMSvP--f2E0=VdMbjE8oibvy921m8JASf4kaCCuU2RA@mail.gmail.com> (raw) There is ongoing work by Yichao Yu to make rr, a userspace record and replay debugger[0], production quality on arm64[1]. One of the bigger remaining issues is the kernel's emulation of accesses to certain system registers[2] that reflect timing and CPU capabilities and are either non-deterministic or can vary from processor to processor. We would like to add the ability to tell the kernel to decline to emulate these instructions for a given task and pass that responsibility onto the supervising rr ptracer. There are analogous processor features and disabling mechanisms on x86. The RDTSC instruction is controlled by prctl(PR_SET_TSC) and the CPUID instruction is controlled (when the hardware allows) by arch_prctl(ARCH_SET_CPUID). The questions I'd like to raise are: 1. Is it appropriate to reuse PR_SET_TSC for roughly equivalent functionality on AArch64? (even if the AArch64 feature is not actually named Time Stamp Counter). 2. Likewise for ARCH_SET_CPUID 3. Since arch_prctl is x86-only, does it make more sense to add arch_prctl to arm64 or to duplicate ARCH_SET_CPUID into the prctl world? (e.g. a PR_SET_CPUID that works on both x86/arm64) - Kyle [0] https://rr-project.org/ [1] https://github.com/rr-debugger/rr/issues/3234 [2] e.g. CNTVCT_EL0 and MIDR_EL1, among others _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next reply other threads:[~2022-05-21 20:07 UTC|newest] Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-05-21 20:07 Kyle Huey [this message] 2022-05-21 20:07 ` arm64 equivalents of PR_SET_TSC/ARCH_SET_CPUID Kyle Huey 2022-05-22 15:35 ` Marc Zyngier 2022-05-22 15:35 ` Marc Zyngier 2022-05-22 18:22 ` Keno Fischer 2022-05-22 18:22 ` Keno Fischer 2022-05-23 19:27 ` Kyle Huey 2022-05-23 19:27 ` Kyle Huey
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