linux-kernel - Re: [PATCH v3 07/16] x86/kvm/emulate: Introduce EM_ASM

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Message-ID: <aIF7ZhWZxlkcpm4y@google.com>
Date: Wed, 23 Jul 2025 17:16:38 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: x86@...nel.org, kys@...rosoft.com, haiyangz@...rosoft.com, 
	wei.liu@...nel.org, decui@...rosoft.com, tglx@...utronix.de, mingo@...hat.com, 
	bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com, pbonzini@...hat.com, 
	ardb@...nel.org, kees@...nel.org, Arnd Bergmann <arnd@...db.de>, 
	gregkh@...uxfoundation.org, jpoimboe@...nel.org, linux-hyperv@...r.kernel.org, 
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, linux-efi@...r.kernel.org, 
	samitolvanen@...gle.com, ojeda@...nel.org
Subject: Re: [PATCH v3 07/16] x86/kvm/emulate: Introduce EM_ASM_1SRC2

For all of the KVM patches, please use

  KVM: x86:

"x86/kvm" is used for guest-side code, and while I hope no one will conflate this
with guest code, the consistency is helpful.

On Mon, Jul 14, 2025, Peter Zijlstra wrote:
> Replace the FASTOP1SRC2*() instructions.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  arch/x86/kvm/emulate.c |   34 ++++++++++++++++++++++++++--------
>  1 file changed, 26 insertions(+), 8 deletions(-)
> 
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -317,6 +317,24 @@ static int em_##op(struct x86_emulate_ct
>  	ON64(case 8: __EM_ASM_1(op##q, rax); break;) \
>  	EM_ASM_END
>  
> +/* 1-operand, using "c" (src2) */
> +#define EM_ASM_1SRC2(op, name) \
> +	EM_ASM_START(name) \
> +	case 1: __EM_ASM_1(op##b, cl); break; \
> +	case 2: __EM_ASM_1(op##w, cx); break; \
> +	case 4: __EM_ASM_1(op##l, ecx); break; \
> +	ON64(case 8: __EM_ASM_1(op##q, rcx); break;) \
> +	EM_ASM_END
> +
> +/* 1-operand, using "c" (src2) with exception */
> +#define EM_ASM_1SRC2EX(op, name) \
> +	EM_ASM_START(name) \
> +	case 1: __EM_ASM_1_EX(op##b, cl); break; \
> +	case 2: __EM_ASM_1_EX(op##w, cx); break; \
> +	case 4: __EM_ASM_1_EX(op##l, ecx); break; \
> +	ON64(case 8: __EM_ASM_1(op##q, rcx); break;) \

This needs to be __EM_ASM_1_EX().  Luckily, KVM-Unit-Tests actually has testcase
for divq (somewhere in the morass of testcases).  I also now have an extension to
the fastops selftest to explicitly test all four flavors of div-by-zero; I'll get
it posted tomorrow.

(also, don't also me how long it took me to spot the copy+paste typo; I was full
 on debugging the exception fixup code before I realized my local diff looked
 "odd", *sigh*)