[PATCH 6.10 621/809] KVM: nVMX: Add a helper to get highest pending from Posted Interrupt vector

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6.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Sean Christopherson <seanjc@xxxxxxxxxx>

commit d83c36d822be44db4bad0c43bea99c8908f54117 upstream.

Add a helper to retrieve the highest pending vector given a Posted
Interrupt descriptor.  While the actual operation is straightforward, it's
surprisingly easy to mess up, e.g. if one tries to reuse lapic.c's
find_highest_vector(), which doesn't work with PID.PIR due to the APIC's
IRR and ISR component registers being physically discontiguous (they're
4-byte registers aligned at 16-byte intervals).

To make PIR handling more consistent with respect to IRR and ISR handling,
return -1 to indicate "no interrupt pending".

Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20240607172609.3205077-2-seanjc@xxxxxxxxxx
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/x86/kvm/vmx/nested.c      |    5 +++--
 arch/x86/kvm/vmx/posted_intr.h |   10 ++++++++++
 2 files changed, 13 insertions(+), 2 deletions(-)

--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -12,6 +12,7 @@
 #include "mmu.h"
 #include "nested.h"
 #include "pmu.h"
+#include "posted_intr.h"
 #include "sgx.h"
 #include "trace.h"
 #include "vmx.h"
@@ -3899,8 +3900,8 @@ static int vmx_complete_nested_posted_in
 	if (!pi_test_and_clear_on(vmx->nested.pi_desc))
 		return 0;
 
-	max_irr = find_last_bit((unsigned long *)vmx->nested.pi_desc->pir, 256);
-	if (max_irr != 256) {
+	max_irr = pi_find_highest_vector(vmx->nested.pi_desc);
+	if (max_irr > 0) {
 		vapic_page = vmx->nested.virtual_apic_map.hva;
 		if (!vapic_page)
 			goto mmio_needed;
--- a/arch/x86/kvm/vmx/posted_intr.h
+++ b/arch/x86/kvm/vmx/posted_intr.h
@@ -1,6 +1,8 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 #ifndef __KVM_X86_VMX_POSTED_INTR_H
 #define __KVM_X86_VMX_POSTED_INTR_H
+
+#include <linux/find.h>
 #include <asm/posted_intr.h>
 
 void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu);
@@ -12,4 +14,12 @@ int vmx_pi_update_irte(struct kvm *kvm,
 		       uint32_t guest_irq, bool set);
 void vmx_pi_start_assignment(struct kvm *kvm);
 
+static inline int pi_find_highest_vector(struct pi_desc *pi_desc)
+{
+	int vec;
+
+	vec = find_last_bit((unsigned long *)pi_desc->pir, 256);
+	return vec < 256 ? vec : -1;
+}
+
 #endif /* __KVM_X86_VMX_POSTED_INTR_H */






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