KVM: SVM: Move lock-protected allocation of SEV ASID into a separate helper

Extract the lock-protected parts of SEV ASID allocation into a new helper
and opportunistically convert it to use guard() when acquiring the mutex.

Preserve the goto even though it's a little odd, as it's there's a fair
amount of subtlety that makes it surprisingly difficult to replicate the
functionality with a loop construct, and arguably using goto yields the
most readable code.

No functional change intended.

Signed-off-by: Carlos López <clopez@suse.de>
[sean: move code to separate helper, rework shortlog+changelog]
Link: https://patch.msgid.link/20260310234829.2608037-21-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 4bf7b2c6b148e22bd81da22856daacff606ee00b..1567d01ef464e72726eae0196099409034b70e89 100644 (file)
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -237,6 +237,28 @@ static void sev_misc_cg_uncharge(struct kvm_sev_info *sev)
        misc_cg_uncharge(type, sev->misc_cg, 1);
 }
 
+static unsigned int sev_alloc_asid(unsigned int min_asid, unsigned int max_asid)
+{
+       unsigned int asid;
+       bool retry = true;
+
+       guard(mutex)(&sev_bitmap_lock);
+
+again:
+       asid = find_next_zero_bit(sev_asid_bitmap, max_asid + 1, min_asid);
+       if (asid > max_asid) {
+               if (retry && __sev_recycle_asids(min_asid, max_asid)) {
+                       retry = false;
+                       goto again;
+               }
+
+               return asid;
+       }
+
+       __set_bit(asid, sev_asid_bitmap);
+       return asid;
+}
+
 static int sev_asid_new(struct kvm_sev_info *sev, unsigned long vm_type)
 {
        /*
@@ -244,7 +266,6 @@ static int sev_asid_new(struct kvm_sev_info *sev, unsigned long vm_type)
         * SEV-ES-enabled guest can use from 1 to min_sev_asid - 1.
         */
        unsigned int min_asid, max_asid, asid;
-       bool retry = true;
        int ret;
 
        if (vm_type == KVM_X86_SNP_VM) {
@@ -277,24 +298,12 @@ static int sev_asid_new(struct kvm_sev_info *sev, unsigned long vm_type)
                return ret;
        }
 
-       mutex_lock(&sev_bitmap_lock);
-
-again:
-       asid = find_next_zero_bit(sev_asid_bitmap, max_asid + 1, min_asid);
+       asid = sev_alloc_asid(min_asid, max_asid);
        if (asid > max_asid) {
-               if (retry && __sev_recycle_asids(min_asid, max_asid)) {
-                       retry = false;
-                       goto again;
-               }
-               mutex_unlock(&sev_bitmap_lock);
                ret = -EBUSY;
                goto e_uncharge;
        }
 
-       __set_bit(asid, sev_asid_bitmap);
-
-       mutex_unlock(&sev_bitmap_lock);
-
        sev->asid = asid;
        return 0;
 e_uncharge: