linux-kernel - Re: [PATCH 6/7] KVM: selftests: Verify guest debug DR7.GD checking during instruction emulation

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Message-ID: <aTMipH-_x4WQVzSL@google.com>
Date: Fri, 5 Dec 2025 10:21:24 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Hou Wenlong <houwenlong.hwl@...group.com>
Cc: kvm@...r.kernel.org, Lai Jiangshan <jiangshan.ljs@...group.com>, 
	Paolo Bonzini <pbonzini@...hat.com>, Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/7] KVM: selftests: Verify guest debug DR7.GD checking
 during instruction emulation

On Wed, Sep 10, 2025, Hou Wenlong wrote:
> Similar to the global disable test case in x86's debug_regs test, use
> 'KVM_FEP' to trigger instruction emulation in order to verify the guest
> debug DR7.GD checking during instruction emulation.
> 
> Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>
> ---
>  tools/testing/selftests/kvm/x86/debug_regs.c | 25 +++++++++++++++++++-
>  1 file changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/kvm/x86/debug_regs.c b/tools/testing/selftests/kvm/x86/debug_regs.c
> index 2d814c1d1dc4..ba80b77c2869 100644
> --- a/tools/testing/selftests/kvm/x86/debug_regs.c
> +++ b/tools/testing/selftests/kvm/x86/debug_regs.c
> @@ -19,6 +19,7 @@
>  uint32_t guest_value;
>  
>  extern unsigned char sw_bp, hw_bp, write_data, ss_start, bd_start;
> +extern unsigned char fep_bd_start;
>  
>  static void guest_code(void)
>  {
> @@ -64,6 +65,12 @@ static void guest_code(void)
>  
>  	/* DR6.BD test */
>  	asm volatile("bd_start: mov %%dr0, %%rax" : : : "rax");
> +
> +	if (is_forced_emulation_enabled) {
> +		/* DR6.BD test for emulation */

Put the comment above the if-statement, that way there's no need for curly braces.
Or just drop it entirely; unless the comments more verbose, I don't think it adds
much value.

> +		asm volatile(KVM_FEP "fep_bd_start: mov %%dr0, %%rax" : : : "rax");
> +	}
> +
>  	GUEST_DONE();
>  }
>  
> @@ -185,7 +192,7 @@ int main(void)
>  			    target_dr6);
>  	}
>  
> -	/* Finally test global disable */
> +	/* test global disable */
>  	memset(&debug, 0, sizeof(debug));
>  	debug.control = KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_HW_BP;
>  	debug.arch.debugreg[7] = 0x400 | DR7_GD;
> @@ -202,6 +209,22 @@ int main(void)
>  			    run->debug.arch.pc, target_rip, run->debug.arch.dr6,
>  			    target_dr6);
>  
> +	/* test global disable in emulation */
> +	if (is_forced_emulation_enabled) {
> +		/* Skip the 3-bytes "mov dr0" */
> +		vcpu_skip_insn(vcpu, 3);
> +		vcpu_run(vcpu);
> +		TEST_ASSERT(run->exit_reason == KVM_EXIT_DEBUG &&
> +			    run->debug.arch.exception == DB_VECTOR &&
> +			    run->debug.arch.pc == CAST_TO_RIP(fep_bd_start) &&
> +			    run->debug.arch.dr6 == target_dr6,
> +			    "DR7.GD: exit %d exception %d rip 0x%llx "
> +			    "(should be 0x%llx) dr6 0x%llx (should be 0x%llx)",
> +			    run->exit_reason, run->debug.arch.exception,
> +			    run->debug.arch.pc, target_rip, run->debug.arch.dr6,
> +			    target_dr6);
> +	}
> +
>  	/* Disable all debug controls, run to the end */
>  	memset(&debug, 0, sizeof(debug));
>  	vcpu_guest_debug_set(vcpu, &debug);
> -- 
> 2.31.1
>