[PATCH 2/3] KVM: x86: Simplify APIC ID selection in kvm_recalculate_phys_map()

Michal Luczaj
2023-05-25T18:36:18Z

Move the comments and condense the code.
No functional change intended.

Signed-off-by: Michal Luczaj <mhal@rbox.co>
---
Perhaps, as it was suggested by Maxim in [1], it would be a good moment to
change kvm_recalculate_phys_map() to return bool?

https://lore.kernel.org/kvm/e90e4c4bd558b9e41acea9f8ce84783e7341c9b4.camel@redhat.com/

arch/x86/kvm/lapic.c | 42 ++++++++++++++++--------------------------
1 file changed, 16 insertions(+), 26 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 39b9a318d04c..7db1c698f6da 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -223,10 +223,10 @@ static int kvm_recalculate_phys_map(struct kvm_apic_map *new,
struct kvm_vcpu *vcpu,
bool *xapic_id_mismatch)
{
+ bool x2format = vcpu->kvm->arch.x2apic_format;
struct kvm_lapic *apic = vcpu->arch.apic;
u32 x2apic_id = kvm_x2apic_id(apic);
u32 xapic_id = kvm_xapic_id(apic);
- u32 physical_id;

/*
* Deliberately truncate the vCPU ID when detecting a mismatched APIC
@@ -250,34 +250,24 @@ static int kvm_recalculate_phys_map(struct kvm_apic_map *new,
* effective APIC ID, e.g. due to the x2APIC wrap or because the guest
* manually modified its xAPIC IDs, events targeting that ID are
* supposed to be recognized by all vCPUs with said ID.
+ *
+ * For !x2apic_format disable the optimized map if the physical APIC ID
+ * is already mapped, i.e. is aliased to multiple vCPUs. The optimized
+ * map requires a strict 1:1 mapping between IDs and vCPUs.
+ *
+ * See also kvm_apic_match_physical_addr().
*/
- if (vcpu->kvm->arch.x2apic_format) {
- /* See also kvm_apic_match_physical_addr(). */
- if ((apic_x2apic_mode(apic) || x2apic_id > 0xff) &&
- x2apic_id <= new->max_apic_id)
- new->phys_map[x2apic_id] = apic;
-
- if (!apic_x2apic_mode(apic) && !new->phys_map[xapic_id])
- new->phys_map[xapic_id] = apic;
- } else {
- /*
- * Disable the optimized map if the physical APIC ID is already
- * mapped, i.e. is aliased to multiple vCPUs. The optimized
- * map requires a strict 1:1 mapping between IDs and vCPUs.
- */
- if (apic_x2apic_mode(apic)) {
- if (x2apic_id > new->max_apic_id)
- return -EINVAL;
+ if (apic_x2apic_mode(apic) || (x2format && x2apic_id > 0xff)) {
+ if (x2apic_id > new->max_apic_id ||
+ (!x2format && new->phys_map[x2apic_id]))
+ return !x2format;

- physical_id = x2apic_id;
- } else {
- physical_id = xapic_id;
- }
-
- if (new->phys_map[physical_id])
- return -EINVAL;
+ new->phys_map[x2apic_id] = apic;
+ } else {
+ if (new->phys_map[xapic_id])
+ return !x2format;

- new->phys_map[physical_id] = apic;
+ new->phys_map[xapic_id] = apic;
}

return 0;
--
2.40.1