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

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Message-ID: <db704530-e4ae-43af-8de4-bcc431f325a2@oracle.com>
Date: Tue, 29 Apr 2025 17:31:18 +0100
From: Liam Merwick <liam.merwick@...cle.com>
To: Sean Christopherson <seanjc@...gle.com>,
        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>, liam.merwick@...cle.com
Subject: Re: [PATCH] KVM: SVM: Update dump_ghcb() to use the GHCB snapshot
 fields



On 29/04/2025 16:22, Sean Christopherson wrote:
> 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);

Would printing "GHCB snapshot (GPA= ...." here instead of just "GHCB 
(GPA= ..."
help gently remind people just looking at the debug output of this too?

Either way, for patch:
Reviewed-by: Liam Merwick <liam.merwick@...cle.com>


>>   	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);
>>   }
>