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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Catalin Marinas writes: > On Fri, Dec 17, 2021 at 08:42:01AM -0800, D Scott Phillips wrote: >> Catalin Marinas writes: >> > On Thu, Dec 16, 2021 at 11:16:18AM -0800, D Scott Phillips wrote: >> >> diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h >> >> index 97932fbf973d..24036b914226 100644 >> >> --- a/arch/arm64/include/asm/elf.h >> >> +++ b/arch/arm64/include/asm/elf.h >> >> @@ -160,8 +160,16 @@ typedef struct user_fpsimd_state elf_fpregset_t; >> >> >> >> #define SET_PERSONALITY(ex) \ >> >> ({ \ >> >> + if (IS_ENABLED(CONFIG_ARM64_ERRATUM_1418040)) \ >> >> + preempt_disable(); \ >> >> clear_thread_flag(TIF_32BIT); \ >> >> current->personality &= ~READ_IMPLIES_EXEC; \ >> >> + if (IS_ENABLED(CONFIG_ARM64_ERRATUM_1418040)) { \ >> >> + if (this_cpu_has_cap(ARM64_WORKAROUND_1418040)) \ >> >> + sysreg_clear_set(cntkctl_el1, 0, \ >> >> + ARCH_TIMER_USR_VCT_ACCESS_EN); \ >> >> + preempt_enable(); \ >> >> + } \ >> >> }) >> >> >> >> /* update AT_VECTOR_SIZE_ARCH if the number of NEW_AUX_ENT entries changes */ >> >> @@ -223,7 +231,16 @@ int compat_elf_check_arch(const struct elf32_hdr *); >> >> */ >> >> #define COMPAT_SET_PERSONALITY(ex) \ >> >> ({ \ >> >> + if (IS_ENABLED(CONFIG_ARM64_ERRATUM_1418040)) \ >> >> + preempt_disable(); \ >> >> set_thread_flag(TIF_32BIT); \ >> >> + if (IS_ENABLED(CONFIG_ARM64_ERRATUM_1418040)) { \ >> >> + if (this_cpu_has_cap(ARM64_WORKAROUND_1418040)) \ >> >> + sysreg_clear_set(cntkctl_el1, \ >> >> + ARCH_TIMER_USR_VCT_ACCESS_EN, \ >> >> + 0); \ >> >> + preempt_enable(); \ >> >> + } \ >> > >> > I don't particularly like adding more to these macros. There's >> > arch_setup_new_exec() that gets called after SET_PERSONALITY, so you can >> > check whether the task is compat or not. >> >> If the task is preemptible between the update to TIF_32BIT and the >> update to cntkctl then a window exists where preemption will confuse the >> workaround logic we have in switch_to, causing the desync between compat >> state and counter access trapping to propagate into other tasks. >> >> Agreed that this change gunks up a previously simple macro though. Maybe >> we could have SET_PERSONALITY only set a flag in arch_elf_state and >> arch_setup_new_exec() take over setting TIF_32BIT? Or move >> set_personality's implementation to a helper? Or something else? > > Is reading ckntkctl_el1 as expensive as the write? If not we could > change the __switch_to() logic to simply check that the bit is set or > cleared depending on is_compat_thread() and skip the comparison with the > previous task. Ah, yes that's a good idea. From a quick check on an N1 core, it looks like reading cntkctl has about the same time cost as reading a general purpose register. I'd assume the other cores affected by the erratum would be similar, so I'll go that route. Thanks, Scott > -- > Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel