This is a note to let you know that I've just added the patch titled
KVM: SVM: Fix a benign off-by-one bug in AVIC physical table mask
to the 6.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
kvm-svm-fix-a-benign-off-by-one-bug-in-avic-physical-table-mask.patch
and it can be found in the queue-6.2 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 3ec7a1b2743c07c45f4a0c508114f6cb410ddef3 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <seanjc@xxxxxxxxxx>
Date: Tue, 7 Feb 2023 00:21:54 +0000
Subject: KVM: SVM: Fix a benign off-by-one bug in AVIC physical table mask
From: Sean Christopherson <seanjc@xxxxxxxxxx>
commit 3ec7a1b2743c07c45f4a0c508114f6cb410ddef3 upstream.
Define the "physical table max index mask" as bits 8:0, not 9:0. x2AVIC
currently supports a max of 512 entries, i.e. the max index is 511, and
the inputs to GENMASK_ULL() are inclusive. The bug is benign as bit 9 is
reserved and never set by KVM, i.e. KVM is just clearing bits that are
guaranteed to be zero.
Note, as of this writing, APM "Rev. 3.39-October 2022" incorrectly states
that bits 11:8 are reserved in Table B-1. VMCB Layout, Control Area. I.e.
that table wasn't updated when x2AVIC support was added.
Opportunistically fix the comment for the max AVIC ID to align with the
code, and clean up comment formatting too.
Fixes: 4d1d7942e36a ("KVM: SVM: Introduce logic to (de)activate x2AVIC mode")
Cc: stable@xxxxxxxxxxxxxxx
Cc: Alejandro Jimenez <alejandro.j.jimenez@xxxxxxxxxx>
Cc: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
Tested-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
Message-Id: <20230207002156.521736-2-seanjc@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/include/asm/svm.h | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
--- a/arch/x86/include/asm/svm.h
+++ b/arch/x86/include/asm/svm.h
@@ -261,20 +261,22 @@ enum avic_ipi_failure_cause {
AVIC_IPI_FAILURE_INVALID_BACKING_PAGE,
};
-#define AVIC_PHYSICAL_MAX_INDEX_MASK GENMASK_ULL(9, 0)
+#define AVIC_PHYSICAL_MAX_INDEX_MASK GENMASK_ULL(8, 0)
/*
- * For AVIC, the max index allowed for physical APIC ID
- * table is 0xff (255).
+ * For AVIC, the max index allowed for physical APIC ID table is 0xfe (254), as
+ * 0xff is a broadcast to all CPUs, i.e. can't be targeted individually.
*/
#define AVIC_MAX_PHYSICAL_ID 0XFEULL
/*
- * For x2AVIC, the max index allowed for physical APIC ID
- * table is 0x1ff (511).
+ * For x2AVIC, the max index allowed for physical APIC ID table is 0x1ff (511).
*/
#define X2AVIC_MAX_PHYSICAL_ID 0x1FFUL
+static_assert((AVIC_MAX_PHYSICAL_ID & AVIC_PHYSICAL_MAX_INDEX_MASK) == AVIC_MAX_PHYSICAL_ID);
+static_assert((X2AVIC_MAX_PHYSICAL_ID & AVIC_PHYSICAL_MAX_INDEX_MASK) == X2AVIC_MAX_PHYSICAL_ID);
+
#define AVIC_HPA_MASK ~((0xFFFULL << 52) | 0xFFF)
#define VMCB_AVIC_APIC_BAR_MASK 0xFFFFFFFFFF000ULL
Patches currently in stable-queue which might be from seanjc@xxxxxxxxxx are
queue-6.2/kvm-svm-modify-avic-gatag-to-support-max-number-of-512-vcpus.patch
queue-6.2/kvm-svm-fix-a-benign-off-by-one-bug-in-avic-physical-table-mask.patch
