linux-kernel - Re: [PATCH RFC 4/5] x86: KVM: add xsetbv to the emulator

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Date:   Wed, 31 Jul 2019 15:14:54 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Radim Krčmář <rkrcmar@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH RFC 4/5] x86: KVM: add xsetbv to the emulator

On 31/07/19 15:07, Vitaly Kuznetsov wrote:
> Paolo Bonzini <pbonzini@...hat.com> writes:
> 
>> On 20/06/19 13:02, Vitaly Kuznetsov wrote:
>>> To avoid hardcoding xsetbv length to '3' we need to support decoding it in
>>> the emulator.
>>>
>>> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>>
>> Can you also emulate it properly?  The code from QEMU's
>> target/i386/fpu_helper.c can help. :)
>>
> 
> (Had a chance to get back to this just now, sorry)
> 
> Assuming __kvm_set_xcr() is also a correct implementation, would the
> code below do the job? (Just trying to figure out why you suggested
> me to take a look at QEMU's variant):
> 

Yes, I didn't remember __kvm_set_xcr.

Paolo

> diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
> index feab24cac610..77cf6c11f66b 100644
> --- a/arch/x86/include/asm/kvm_emulate.h
> +++ b/arch/x86/include/asm/kvm_emulate.h
> @@ -229,7 +229,7 @@ struct x86_emulate_ops {
>  	int (*pre_leave_smm)(struct x86_emulate_ctxt *ctxt,
>  			     const char *smstate);
>  	void (*post_leave_smm)(struct x86_emulate_ctxt *ctxt);
> -
> +	int (*set_xcr)(struct x86_emulate_ctxt *ctxt, u32 index, u64 xcr);
>  };
>  
>  typedef u32 __attribute__((vector_size(16))) sse128_t;
> @@ -429,6 +429,7 @@ enum x86_intercept {
>  	x86_intercept_ins,
>  	x86_intercept_out,
>  	x86_intercept_outs,
> +	x86_intercept_xsetbv,
>  
>  	nr_x86_intercepts
>  };
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 718f7d9afedc..f9e843dd992a 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -4156,6 +4156,20 @@ static int em_fxrstor(struct x86_emulate_ctxt *ctxt)
>  	return rc;
>  }
>  
> +static int em_xsetbv(struct x86_emulate_ctxt *ctxt)
> +{
> +	u32 eax, ecx, edx;
> +
> +	eax = reg_read(ctxt, VCPU_REGS_RAX);
> +	edx = reg_read(ctxt, VCPU_REGS_RDX);
> +	ecx = reg_read(ctxt, VCPU_REGS_RCX);
> +
> +	if (ctxt->ops->set_xcr(ctxt, ecx, ((u64)edx << 32) | eax))
> +		return emulate_gp(ctxt, 0);
> +
> +	return X86EMUL_CONTINUE;
> +}
> +
>  static bool valid_cr(int nr)
>  {
>  	switch (nr) {
> @@ -4409,6 +4423,12 @@ static const struct opcode group7_rm1[] = {
>  	N, N, N, N, N, N,
>  };
>  
> +static const struct opcode group7_rm2[] = {
> +	N,
> +	II(ImplicitOps | Priv,			em_xsetbv,	xsetbv),
> +	N, N, N, N, N, N,
> +};
> +
>  static const struct opcode group7_rm3[] = {
>  	DIP(SrcNone | Prot | Priv,		vmrun,		check_svme_pa),
>  	II(SrcNone  | Prot | EmulateOnUD,	em_hypercall,	vmmcall),
> @@ -4498,7 +4518,8 @@ static const struct group_dual group7 = { {
>  }, {
>  	EXT(0, group7_rm0),
>  	EXT(0, group7_rm1),
> -	N, EXT(0, group7_rm3),
> +	EXT(0, group7_rm2),
> +	EXT(0, group7_rm3),
>  	II(SrcNone | DstMem | Mov,		em_smsw, smsw), N,
>  	II(SrcMem16 | Mov | Priv,		em_lmsw, lmsw),
>  	EXT(0, group7_rm7),
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c6d951cbd76c..9512cc38dfe9 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6068,6 +6068,11 @@ static void emulator_post_leave_smm(struct x86_emulate_ctxt *ctxt)
>  	kvm_smm_changed(emul_to_vcpu(ctxt));
>  }
>  
> +static int emulator_set_xcr(struct x86_emulate_ctxt *ctxt, u32 index, u64 xcr)
> +{
> +	return __kvm_set_xcr(emul_to_vcpu(ctxt), index, xcr);
> +}
> +
>  static const struct x86_emulate_ops emulate_ops = {
>  	.read_gpr            = emulator_read_gpr,
>  	.write_gpr           = emulator_write_gpr,
> @@ -6109,6 +6114,7 @@ static const struct x86_emulate_ops emulate_ops = {
>  	.set_hflags          = emulator_set_hflags,
>  	.pre_leave_smm       = emulator_pre_leave_smm,
>  	.post_leave_smm      = emulator_post_leave_smm,
> +	.set_xcr             = emulator_set_xcr,
>  };
>  
>  static void toggle_interruptibility(struct kvm_vcpu *vcpu, u32 mask)
>