linux-kernel - [PATCH v9 03/15] KVM: xen: mark guest pages dirty with the pfncache lock held

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Date:   Wed, 22 Nov 2023 12:18:10 +0000
From:   Paul Durrant <paul@....org>
To:     David Woodhouse <dwmw2@...radead.org>, Paul Durrant <paul@....org>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v9 03/15] KVM: xen: mark guest pages dirty with the pfncache lock held

From: Paul Durrant <pdurrant@...zon.com>

Sampling gpa and memslot from an unlocked pfncache may yield inconsistent
values so, since there is no problem with calling mark_page_dirty_in_slot()
with the pfncache lock held, relocate the calls in
kvm_xen_update_runstate_guest() and kvm_xen_inject_pending_events()
accordingly.

Signed-off-by: Paul Durrant <pdurrant@...zon.com>
Reviewed-by: David Woodhouse <dwmw@...zon.co.uk>
---
Cc: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: David Woodhouse <dwmw2@...radead.org>
Cc: x86@...nel.org

v8:
 - New in this version.
---
 arch/x86/kvm/xen.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index e53fad915a62..426306022c2f 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -452,14 +452,13 @@ static void kvm_xen_update_runstate_guest(struct kvm_vcpu *v, bool atomic)
 		smp_wmb();
 	}
 
-	if (user_len2)
+	if (user_len2) {
+		mark_page_dirty_in_slot(v->kvm, gpc2->memslot, gpc2->gpa >> PAGE_SHIFT);
 		read_unlock(&gpc2->lock);
-
-	read_unlock_irqrestore(&gpc1->lock, flags);
+	}
 
 	mark_page_dirty_in_slot(v->kvm, gpc1->memslot, gpc1->gpa >> PAGE_SHIFT);
-	if (user_len2)
-		mark_page_dirty_in_slot(v->kvm, gpc2->memslot, gpc2->gpa >> PAGE_SHIFT);
+	read_unlock_irqrestore(&gpc1->lock, flags);
 }
 
 void kvm_xen_update_runstate(struct kvm_vcpu *v, int state)
@@ -565,13 +564,13 @@ void kvm_xen_inject_pending_events(struct kvm_vcpu *v)
 			     : "0" (evtchn_pending_sel32));
 		WRITE_ONCE(vi->evtchn_upcall_pending, 1);
 	}
+
+	mark_page_dirty_in_slot(v->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
 	read_unlock_irqrestore(&gpc->lock, flags);
 
 	/* For the per-vCPU lapic vector, deliver it as MSI. */
 	if (v->arch.xen.upcall_vector)
 		kvm_xen_inject_vcpu_vector(v);
-
-	mark_page_dirty_in_slot(v->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
 }
 
 int __kvm_xen_has_interrupt(struct kvm_vcpu *v)
-- 
2.39.2