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Re: [PATCH v1 04/28] x86/hvm: avic: add domain state initialization

To: <dmukhin@xxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>

From: Jason Andryuk <jason.andryuk@xxxxxxx>

Date: Thu, 5 Nov 2026 20:35:25 -0500

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Cc: <andrew.cooper3@xxxxxxxxxx>, <jbeulich@xxxxxxxx>, <roger@xxxxxxxxxxxxxx>, <teddy.astie@xxxxxxxxxx>, <dmukhin@xxxxxxx>

Delivery-date: Fri, 06 Nov 2026 01:35:44 +0000

List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 2026-11-05 18:10, Jason Andryuk wrote:

On 2026-11-04 20:33, dmukhin@xxxxxxxx wrote:

From: Denis Mukhin <dmukhin@xxxxxxxx>

Establish per-domain SVM AVIC backing page mapping and SPA mappings
for APIC physical/logical ID tables. Use MEMF_no_refcount mappings
similarly to Intel's VMX APICv setup.

Gate per-domain AVIC state initialization behind 'svm_avic=' command
line option.


AIUI, "-" is preferred, so 'svm-avic='.

+
+/*
+ * Enable guest accesses to APIC_DEFAULT_PHYS_BASE.
+ *
+ * AVIC walks the nested page table to check access permissions, but
+ * ignores the SPA from the leaf entry and instead uses the address in
+ * VMCB.avic_backing_page.
+ *
+ * Install a mapping so APIC accesses don't trap to Xen while xAPIC is
+ * accelerated.

Now I have a question. Why don't we eventually just use

VMCB.avic_backing_page itself?

Regards, Jason

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