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From: Sean Christopherson <seanjc@google.com>
To: Alexey Kardashevskiy <aik@amd.com>
Cc: kvm@vger.kernel.org, x86@kernel.org,
	linux-kernel@vger.kernel.org,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Santosh Shukla <santosh.shukla@amd.com>
Subject: Re: [PATCH kernel 5/9] KVM: SVM/SEV/SEV-ES: Rework intercepts
Date: Fri, 30 Jun 2023 14:49:16 -0700	[thread overview]
Message-ID: <ZJ9N3GMNuKJXc5wQ@google.com> (raw)
In-Reply-To: <20230615063757.3039121-6-aik@amd.com>

On Thu, Jun 15, 2023, Alexey Kardashevskiy wrote:
> @@ -2976,6 +2977,16 @@ static void sev_es_init_vmcb(struct vcpu_svm *svm)
>  	svm_set_intercept(svm, TRAP_CR4_WRITE);
>  	svm_set_intercept(svm, TRAP_CR8_WRITE);
>  
> +	/*
> +	 * DR7 access must remain intercepted for an SEV-ES guest to disallow
> +	 * the guest kernel set up a #DB on memory that's needed to vector a #DB
> +	 * as otherwise the CPU gets stuck in an infinite #DB loop.
> +	 */

This isn't correct.  Letting the guest configuring breakpoints would be weird
and nonsensical, but it wouldn't lead to infinite #DBs so long as KVM intercepts
#DB.

KVM intercepts DR7 when DebugSwap isn't enabled because otherwise KVM has no way
of context switching DR[0-3] for the guest.  At least, I assume that's the case,
AFAICT the APM never actually says what happens with DR[0-3] when DebugSwap is
disabled.

  reply	other threads:[~2023-06-30 21:49 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-06-15  6:37 [PATCH kernel 0/9] KVM: SEV: Enable AMD SEV-ES DebugSwap Alexey Kardashevskiy
2023-06-15  6:37 ` [PATCH kernel 1/9] KVM: SEV: move set_dr_intercepts/clr_dr_intercepts from the header Alexey Kardashevskiy
2023-06-15  6:37 ` [PATCH kernel 2/9] KVM: SEV: Move SEV's GP_VECTOR intercept setup to SEV Alexey Kardashevskiy
2023-06-15  6:37 ` [PATCH kernel 3/9] KVM: SVM: Rewrite sev_es_prepare_switch_to_guest()'s comment about swap types Alexey Kardashevskiy
2023-06-15  6:37 ` [PATCH kernel 4/9] KVM: SEV-ES: explicitly disable debug Alexey Kardashevskiy
2023-06-15  6:37 ` [PATCH kernel 5/9] KVM: SVM/SEV/SEV-ES: Rework intercepts Alexey Kardashevskiy
2023-06-30 21:49   ` Sean Christopherson [this message]
2023-07-03  2:01     ` Alexey Kardashevskiy
2023-06-15  6:37 ` [PATCH kernel 6/9] KVM: SEV: Enable data breakpoints in SEV-ES Alexey Kardashevskiy
2023-06-15  6:37 ` [PATCH kernel 7/9] KVM: SEV-ES: Eliminate #DB intercept when DebugSwap enabled Alexey Kardashevskiy
2023-06-15  6:37 ` [PATCH kernel 8/9] KVM: SVM: Don't defer NMI unblocking until next exit for SEV-ES guests Alexey Kardashevskiy
2023-06-15  6:37 ` [PATCH kernel 9/9] KVM: SVM: Don't try to pointlessly single-step SEV-ES guests for NMI window Alexey Kardashevskiy
2023-06-15  7:13 ` [PATCH kernel 0/9 v6] KVM: SEV: Enable AMD SEV-ES DebugSwap Alexey Kardashevskiy
2023-06-23  1:35   ` Alexey Kardashevskiy
2023-06-23 14:19     ` Sean Christopherson
2023-06-30  2:08       ` Alexey Kardashevskiy
2023-06-30 21:52         ` Sean Christopherson
2023-07-20 19:01           ` Alexey Kardashevskiy
2023-07-28 23:49 ` [PATCH kernel 0/9] " Sean Christopherson
2023-07-29  1:57   ` Alexey Kardashevskiy

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