linux-kernel - [PATCH v4 4/7] KVM: SVM: Expand AVIC_PHYSICAL_MAX_INDEX

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Message-ID: <a464adcfbe48e4d2febf2b0e480231f1f1a56162.1755797611.git.naveen@kernel.org>
Date: Thu, 21 Aug 2025 23:48:35 +0530
From: "Naveen N Rao (AMD)" <naveen@...nel.org>
To: Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>
Cc: <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
	Vasant Hegde <vasant.hegde@....com>,
	Pankaj Gupta <pankaj.gupta@....com>,
	Alejandro Jimenez <alejandro.j.jimenez@...cle.com>,
	Joao Martins <joao.m.martins@...cle.com>,
	Nikunj A Dadhania <nikunj@....com>
Subject: [PATCH v4 4/7] KVM: SVM: Expand AVIC_PHYSICAL_MAX_INDEX_MASK to be a 12-bit field

In the latest APM describing AVIC support for 4k vCPUs, VMCB
AVIC_PHYSICAL_MAX_INDEX (Offset 0xF8) and EXITINFO2.Index are both
updated from 9-bit wide to 12-bit wide fields unconditionally (i.e.,
regardless of AVIC support for 4k vCPUs). Expand
AVIC_PHYSICAL_MAX_INDEX_MASK accordingly.

While AVIC_PHYSICAL_MAX_INDEX_MASK is updated to a 12-bit field, KVM
will limit the max vCPU/APIC ID based on the maximum supported on a
specific processor and enforce that limit during vCPU creation. I.e.,
we don't need to rely on the mask to ensure that the max APIC ID being
programmed in the VMCB is in range. The additional bits (11:9) were
previously marked reserved and were never set/read by older processors.

Signed-off-by: Naveen N Rao (AMD) <naveen@...nel.org>
---
 arch/x86/include/asm/svm.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
index ffc27f676243..58c10991521c 100644
--- a/arch/x86/include/asm/svm.h
+++ b/arch/x86/include/asm/svm.h
@@ -279,7 +279,7 @@ enum avic_ipi_failure_cause {
 	AVIC_IPI_FAILURE_INVALID_IPI_VECTOR,
 };

-#define AVIC_PHYSICAL_MAX_INDEX_MASK	GENMASK_ULL(8, 0)
+#define AVIC_PHYSICAL_MAX_INDEX_MASK	GENMASK_ULL(11, 0)

 /*
  * For AVIC, the max index allowed for physical APIC ID table is 0xfe (254), as
-- 
2.50.1