linux-kernel - [PATCH 22/26] KVM: x86: asi: Stabilize CR3 when potentially accessing with ASI

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Message-ID: <20240712-asi-rfc-24-v1-22-144b319a40d8@google.com>
Date: Fri, 12 Jul 2024 17:00:40 +0000
From: Brendan Jackman <jackmanb@...gle.com>
To: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>, 
	Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	Alexandre Chartre <alexandre.chartre@...cle.com>, Liran Alon <liran.alon@...cle.com>, 
	Jan Setje-Eilers <jan.setjeeilers@...cle.com>, Catalin Marinas <catalin.marinas@....com>, 
	Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Mel Gorman <mgorman@...e.de>, 
	Lorenzo Stoakes <lstoakes@...il.com>, David Hildenbrand <david@...hat.com>, Vlastimil Babka <vbabka@...e.cz>, 
	Michal Hocko <mhocko@...nel.org>, Khalid Aziz <khalid.aziz@...cle.com>, 
	Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>, 
	Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>, 
	Valentin Schneider <vschneid@...hat.com>, Paul Turner <pjt@...gle.com>, Reiji Watanabe <reijiw@...gle.com>, 
	Junaid Shahid <junaids@...gle.com>, Ofir Weisse <oweisse@...gle.com>, 
	Yosry Ahmed <yosryahmed@...gle.com>, Patrick Bellasi <derkling@...gle.com>, 
	KP Singh <kpsingh@...gle.com>, Alexandra Sandulescu <aesa@...gle.com>, 
	Matteo Rizzo <matteorizzo@...gle.com>, Jann Horn <jannh@...gle.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	kvm@...r.kernel.org, Brendan Jackman <jackmanb@...gle.com>
Subject: [PATCH 22/26] KVM: x86: asi: Stabilize CR3 when potentially accessing
 with ASI

nested_vmx_check_vmentry_hw() does a VM Enter as a "dry run" to check
the VMCS. It's important that we VM Exit back into the correct CR3 in
order to avoid going out of sync with ASI state. Under ASI, CR3 is
unstable even when interrupts are disabled, except
a) during the ASI critical section and
b) when the address space is unrestricted. We can take advantage of case
b) here to make sure the VM Enter is safe.

Signed-off-by: Brendan Jackman <jackmanb@...gle.com>
---
 arch/x86/kvm/vmx/nested.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index d05ddf751491..ffca468f8197 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3147,6 +3147,14 @@ static int nested_vmx_check_vmentry_hw(struct kvm_vcpu *vcpu)
 	 */
 	vmcs_writel(GUEST_RFLAGS, 0);
 
+	/*
+	 * Stabilize CR3 to ensure the VM Exit returns to the correct address
+	 * space. This is costly; at the expense of complexity it could be
+	 * optimized away by instead doing an asi_enter() to create an ASI
+	 * critical section, in the case that we are currently restricted.
+	 */
+	asi_exit();
+
 	cr3 = __get_current_cr3_fast();
 	if (unlikely(cr3 != vmx->loaded_vmcs->host_state.cr3)) {
 		vmcs_writel(HOST_CR3, cr3);

-- 
2.45.2.993.g49e7a77208-goog