Messages in this thread | | | Date | Thu, 11 Aug 2022 19:27:10 +0000 | From | Sean Christopherson <> | Subject | Re: [PATCH] x86/asm: Force native_apic_mem_read to use mov |
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On Thu, Aug 11, 2022, Adam Dunlap wrote: > Previously, when compiled with clang, native_apic_mem_read gets inlined > into __xapic_wait_icr_idle and optimized to a testl instruction. When > run in a VM with SEV-ES enabled, it attempts to emulate this > instruction, but the emulator does not support it. Instead, use inline > assembly to force native_apic_mem_read to use the mov instruction which > is supported by the emulator. > > Signed-off-by: Adam Dunlap <acdunlap@google.com> > Reviewed-by: Marc Orr <marcorr@google.com> > Reviewed-by: Jacob Xu <jacobhxu@google.com> > --- > arch/x86/include/asm/apic.h | 13 ++++++++++++- > 1 file changed, 12 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h > index 3415321c8240..281db79e76a9 100644 > --- a/arch/x86/include/asm/apic.h > +++ b/arch/x86/include/asm/apic.h > @@ -109,7 +109,18 @@ static inline void native_apic_mem_write(u32 reg, u32 v) > > static inline u32 native_apic_mem_read(u32 reg) > { > - return *((volatile u32 *)(APIC_BASE + reg)); > + volatile u32 *addr = (volatile u32 *)(APIC_BASE + reg); > + u32 out; > + > + /* > + * Functionally, what we want to do is simply return *addr. However, > + * this accesses an MMIO which may need to be emulated in some cases. > + * The emulator doesn't necessarily support all instructions, so we > + * force the read from addr to use a mov instruction. > + */ > + asm_inline("movl %1, %0" : "=r"(out) : "m"(*addr)); > + > + return out;
Can't this just be:
return readl((void __iomem *)(APIC_BASE + reg));
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