Messages in this thread |  | | Subject | Re: [PATCH v5 02/27] arm64: cpufeature: Use alternatives for VHE cpu_enable | From | Julien Thierry <> | Date | Wed, 12 Sep 2018 13:03:08 +0100 |
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Hi James,
On 12/09/18 11:28, James Morse wrote: > Hi Julien, > > On 28/08/18 16:51, Julien Thierry wrote: >> The cpu_enable callback for VHE feature requires all alternatives to have >> been applied. This prevents applying VHE alternative separately from the >> rest. >> >> Use an alternative depending on VHE feature to know whether VHE >> alternatives have already been applied. > >> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c >> index 1e433ac..3bc1c8b 100644 >> --- a/arch/arm64/kernel/cpufeature.c >> +++ b/arch/arm64/kernel/cpufeature.c >> @@ -1022,8 +1024,15 @@ static void cpu_copy_el2regs(const struct arm64_cpu_capabilities *__unused) >> * that, freshly-onlined CPUs will set tpidr_el2, so we don't need to >> * do anything here. >> */ >> - if (!alternatives_applied) >> - write_sysreg(read_sysreg(tpidr_el1), tpidr_el2); >> + asm volatile(ALTERNATIVE( >> + "mrs %0, tpidr_el1\n" >> + "msr tpidr_el2, %0", >> + "nop\n" >> + "nop", >> + ARM64_HAS_VIRT_HOST_EXTN) >> + : "+r" (tmp) >> + : >> + : "memory"); >> } >> #endif > > Catalin's preference was to keep this all in C: > https://patchwork.kernel.org/patch/10007977/ > , for which we need to know if 'the' alternative has been applied. > > I suspect there may be more registers in this list if we have to switch to > another EL2 register using alternatives. (but I don't have an example). > > Could we make 'alternatives_applied' a macro that takes the cap as an argument? >
I wanted to do this initially, the issue was that the alternatives framework works on regions to patch rather than caps to apply. So I found it a bit odd to associate the "code corresponding to cap was applied" with the alternative application.
Although in patch 3 with the feature mask I guess that at the end of the __apply_alternatives loop, if the cap was part of the mask passed, it can be considered as applied. If the asm inline is problematic I can go that route.
Thanks,
-- Julien Thierry
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