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Date: Fri, 15 Jan 2021 10:53:51 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Jason Baron <jbaron@...mai.com> Cc: pbonzini@...hat.com, seanjc@...gle.com, kvm@...r.kernel.org, x86@...nel.org, linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Andrea Arcangeli <aarcange@...hat.com> Subject: Re: [PATCH v2 3/3] KVM: x86: use static calls to reduce kvm_x86_ops overhead On Fri, Jan 15, 2021 at 10:45:49AM +0100, Peter Zijlstra wrote: > On Thu, Jan 14, 2021 at 10:27:56PM -0500, Jason Baron wrote: > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > > index 5060922..9d4492b 100644 > > --- a/arch/x86/include/asm/kvm_host.h > > +++ b/arch/x86/include/asm/kvm_host.h > > @@ -1350,7 +1350,7 @@ void kvm_arch_free_vm(struct kvm *kvm); > > static inline int kvm_arch_flush_remote_tlb(struct kvm *kvm) > > { > > if (kvm_x86_ops.tlb_remote_flush && > > - !kvm_x86_ops.tlb_remote_flush(kvm)) > > + !static_call(kvm_x86_tlb_remote_flush)(kvm)) > > return 0; > > else > > return -ENOTSUPP; > > Would you be able to use something like this? > > https://lkml.kernel.org/r/20201110101307.GO2651@hirez.programming.kicks-ass.net > > we could also add __static_call_return1(), if that would help. Something like so on top of the above. --- a/arch/x86/kernel/static_call.c +++ b/arch/x86/kernel/static_call.c @@ -17,6 +17,7 @@ static void __ref __static_call_transfor * disp16 disp16 xorq %rax, %rax - a single 5 byte instruction that clears %rax */ static const u8 ret0[5] = { 0x66, 0x66, 0x48, 0x31, 0xc0 }; + static const u8 ret1[5] = { 0xb8, 0x01, 0x00, 0x00, 0x00 }; /* mov $0x1,%eax */ int size = CALL_INSN_SIZE; const void *emulate = NULL; const void *code; @@ -27,7 +28,11 @@ static void __ref __static_call_transfor if (func == &__static_call_return0) { emulate = code; code = ret0; + } else if (func == &__static_call_return1) { + emulate = code; + code = ret1; } + break; case NOP: --- a/include/linux/static_call.h +++ b/include/linux/static_call.h @@ -137,6 +137,7 @@ extern void arch_static_call_transform(v #ifdef CONFIG_HAVE_STATIC_CALL_INLINE extern long __static_call_return0(void); +extern long __static_call_return1(void); extern int __init static_call_init(void); @@ -190,6 +191,7 @@ extern int static_call_text_reserved(voi #elif defined(CONFIG_HAVE_STATIC_CALL) static inline long __static_call_return0(void) { return 0; } +static inline long __static_call_return0(void) { return 1; } static inline int static_call_init(void) { return 0; } @@ -239,6 +241,7 @@ static inline int static_call_text_reser #else /* Generic implementation */ static inline long __static_call_return0(void) { return 0; } +static inline long __static_call_return0(void) { return 1; } static inline int static_call_init(void) { return 0; } --- a/kernel/static_call.c +++ b/kernel/static_call.c @@ -443,6 +443,11 @@ long __static_call_return0(void) return 0; } +long __static_call_return1(void) +{ + return 1; +} + #ifdef CONFIG_STATIC_CALL_SELFTEST static int func_a(int x)
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