linux-kernel - Re: [PATCH] KVM: SVM: Update dump_ghcb() to use the GHCB snapshot fields

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Message-ID: <aBDumDW9kWEotu0A@google.com>
Date: Tue, 29 Apr 2025 08:22:00 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Tom Lendacky <thomas.lendacky@....com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org, 
	Paolo Bonzini <pbonzini@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, Ingo Molnar <mingo@...hat.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Michael Roth <michael.roth@....com>
Subject: Re: [PATCH] KVM: SVM: Update dump_ghcb() to use the GHCB snapshot fields

On Mon, Apr 28, 2025, Tom Lendacky wrote:
> @@ -3184,18 +3189,18 @@ static void dump_ghcb(struct vcpu_svm *svm)
>  		return;
>  	}
>  
> -	nbits = sizeof(ghcb->save.valid_bitmap) * 8;
> +	nbits = sizeof(svm->sev_es.valid_bitmap) * 8;

I'm planning on adding this comment to explain the use of KVM's snapshot.  Please
holler if it's wrong/misleading in any way.

	/*
	 * Print KVM's snapshot of the GHCB that was (unsuccessfully) used to
	 * handle the exit.  If the guest has since modified the GHCB itself,
	 * dumping the raw GHCB won't help debug why KVM was unable to handle
	 * the VMGEXIT that KVM observed.
	 */

>  	pr_err("GHCB (GPA=%016llx):\n", svm->vmcb->control.ghcb_gpa);
>  	pr_err("%-20s%016llx is_valid: %u\n", "sw_exit_code",
> -	       ghcb->save.sw_exit_code, ghcb_sw_exit_code_is_valid(ghcb));
> +	       kvm_ghcb_get_sw_exit_code(control), kvm_ghcb_sw_exit_code_is_valid(svm));
>  	pr_err("%-20s%016llx is_valid: %u\n", "sw_exit_info_1",
> -	       ghcb->save.sw_exit_info_1, ghcb_sw_exit_info_1_is_valid(ghcb));
> +	       control->exit_info_1, kvm_ghcb_sw_exit_info_1_is_valid(svm));
>  	pr_err("%-20s%016llx is_valid: %u\n", "sw_exit_info_2",
> -	       ghcb->save.sw_exit_info_2, ghcb_sw_exit_info_2_is_valid(ghcb));
> +	       control->exit_info_2, kvm_ghcb_sw_exit_info_2_is_valid(svm));
>  	pr_err("%-20s%016llx is_valid: %u\n", "sw_scratch",
> -	       ghcb->save.sw_scratch, ghcb_sw_scratch_is_valid(ghcb));
> -	pr_err("%-20s%*pb\n", "valid_bitmap", nbits, ghcb->save.valid_bitmap);
> +	       svm->sev_es.sw_scratch, kvm_ghcb_sw_scratch_is_valid(svm));
> +	pr_err("%-20s%*pb\n", "valid_bitmap", nbits, svm->sev_es.valid_bitmap);
>  }