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[PATCH] x86/svm: Don't clear clean bits on every context switch
- To: xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
- Date: Tue, 6 Oct 2026 15:48:05 +0100
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- Cc: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger@xxxxxxxxxxxxxx>, Jason Andryuk <jason.andryuk@xxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>
- Delivery-date: Tue, 06 Oct 2026 14:48:37 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
Clear the cleanbits only when the VMCB is used on a different pCPU
rather than on every context switch to the vCPU. This follows the APM
guideline for when to clear the cleanbits:
"The hypervisor executes the guest on a different CPU core than one used
the last time that guest was executed."
Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
---
xen/arch/x86/hvm/svm/svm.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index 71e48351f22c..4e22322f4b42 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -890,7 +890,6 @@ static void cf_check svm_ctxt_switch_from(struct vcpu *v)
static void cf_check svm_ctxt_switch_to(struct vcpu *v)
{
- struct vmcb_struct *vmcb = v->arch.hvm.svm.vmcb;
int cpu = smp_processor_id();
/*
@@ -908,7 +907,6 @@ static void cf_check svm_ctxt_switch_to(struct vcpu *v)
svm_restore_dr(v);
- vmcb->cleanbits.raw = 0;
svm_tsc_ratio_load(v);
if ( cpu_has_msr_tsc_aux )
@@ -953,6 +951,7 @@ static void noreturn cf_check svm_do_resume(void)
hvm_migrate_pirqs(v);
/* Migrating to another ASID domain. Request a new ASID. */
hvm_asid_flush_vcpu(v);
+ vmcb->cleanbits.raw = 0;
}
if ( !vcpu_guestmode && !vlapic_hw_disabled(vlapic) )
--
2.55.0
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