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[PATCH v2 2/7] x86/nestedvmx: Emulate L2 accesses to L1's LAPIC page
- To: xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: chunjie.zhu@xxxxxxxxxx
- Date: Thu, 29 Oct 2026 14:26:54 +0800
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- Cc: andrew.cooper3@xxxxxxxxxx, anthony.perard@xxxxxxxxxx, michal.orzel@xxxxxxx, jbeulich@xxxxxxxx, julien@xxxxxxx, roger@xxxxxxxxxxxxxx, sstabellini@xxxxxxxxxx, dpsmith@xxxxxxxxxxxxxxxxxxxx, Stephen.Cheng@xxxxxxxxxx, Chunjie Zhu <chunjie.zhu@xxxxxxxxxx>
- Delivery-date: Thu, 29 Oct 2026 06:27:50 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
From: Chunjie Zhu <chunjie.zhu@xxxxxxxxxx>
Return NESTEDHVM_PAGEFAULT_MMIO when the L0 p2m entry is the APIC-access
page, so that the access faults and is emulated against L1's vLAPIC.
Signed-off-by: Chunjie Zhu <chunjie.zhu@xxxxxxxxxx>
---
xen/arch/x86/mm/hap/nested_hap.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/xen/arch/x86/mm/hap/nested_hap.c b/xen/arch/x86/mm/hap/nested_hap.c
index 255fba7e1cac..ceabf31ec0ab 100644
--- a/xen/arch/x86/mm/hap/nested_hap.c
+++ b/xen/arch/x86/mm/hap/nested_hap.c
@@ -17,6 +17,7 @@
#include <asm/hap.h>
#include <asm/hvm/nestedhvm.h>
+#include <asm/hvm/vmx/vmcs.h>
#include "private.h"
@@ -115,6 +116,17 @@ static int nestedhap_walk_L0_p2m(
mfn = get_gfn_type_access(p2m, L1_gpa >> PAGE_SHIFT, p2mt, p2ma,
0, page_order);
+ /*
+ * With APIC-access virtualisation, Xen backs the LAPIC page of L1 with a
+ * dummy page. L2 must not touch it directly: the access is to L1's
+ * emulated LAPIC, so let the caller emulate it.
+ */
+ rc = NESTEDHVM_PAGEFAULT_MMIO;
+ if ( *p2mt == p2m_mmio_direct && cpu_has_vmx &&
+ !mfn_eq(p2m->domain->arch.hvm.vmx.apic_access_mfn, _mfn(0)) &&
+ mfn_eq(mfn, p2m->domain->arch.hvm.vmx.apic_access_mfn) )
+ goto out;
+
rc = NESTEDHVM_PAGEFAULT_DIRECT_MMIO;
if ( *p2mt == p2m_mmio_direct )
goto direct_mmio_out;
--
2.34.1
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