Hi Catalin, On 16/10/17 10:58, Catalin Marinas wrote: > On Fri, Oct 13, 2017 at 05:50:45PM +0100, James Morse wrote: >> On 13/10/17 16:31, Catalin Marinas wrote: >>> On Fri, Sep 22, 2017 at 07:26:05PM +0100, James Morse wrote: >>>> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c >>>> index cd52d365d1f0..8e4c7da2b126 100644 >>>> --- a/arch/arm64/kernel/cpufeature.c >>>> +++ b/arch/arm64/kernel/cpufeature.c >> >>>> @@ -1308,3 +1309,25 @@ static int __init enable_mrs_emulation(void) >>>> } >>>> >>>> late_initcall(enable_mrs_emulation); >>>> + >>>> +int cpu_copy_el2regs(void *__unused) >>>> +{ >>>> + int do_copyregs = 0; >>>> + >>>> + /* >>>> + * Copy register values that aren't redirected by hardware. >>>> + * >>>> + * Before code patching, we only set tpidr_el1, all CPUs need to copy >>>> + * this value to tpidr_el2 before we patch the code. Once we've done >>>> + * that, freshly-onlined CPUs will set tpidr_el2, so we don't need to >>>> + * do anything here. >>>> + */ >>>> + asm volatile(ALTERNATIVE("mov %0, #1", "mov %0, #0", >>>> + ARM64_HAS_VIRT_HOST_EXTN) >>>> + : "=r" (do_copyregs) : : ); >>> >>> Can you just do: >>> >>> if (cpu_have_const_cap(ARM64_HAS_VIRT_HOST_EXTN)) >>> write_sysreg(read_sysreg(tpidr_el1), tpidr_el2); >>> >>> At this point the capability bits should be set and the jump labels >>> enabled. >> >> These are enabled too early, we haven't done patching yet. >> >> We need to copy tpidr_el1 -> tpidr_el2 on all CPUs that are online before code >> patching. >> >> After code patching new CPUs set tpidr_el2 when they come online, so we don't >> need to do the copy... but this enable method is still called. There is nothing >> for us to do, and tpidr_el1 now contains junk, so the copy > Ah, I get it now (should've read the comment but I usually expect the > code to be obvious; it wasn't, at least to me, in this case ;)). > You could have added the sysreg copying directly in the asm volatile. I was trying to stick to the sysreg C accessors, and thought there would be more registers that needed copying. (I discovered this VHE doesn't remap all the _ELx registers quite late.) > Anyway, I think it's better if we keep it entirely in C with this hunk > (untested): [...] Yes, that looks much better. I got tangled up in 'which alternative', but you're right, they are all applied in one go so it doesn't matter. > if (!READ_ONCE(alternatives_applied)) > write_sysreg(read_sysreg(tpidr_el1), tpidr_el2); I don't think this READ_ONCE() is needed, that only matters within the stop_machine()/alternatives-patching code that modifies the value on one CPU. Thanks, James -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html