On Mon, Feb 12, 2024 at 11:21:30AM +0100, Heiko Carstens wrote:
> Or maybe a TIF flag with different semantics: "guest save area does not
> reflect current state - which is within registers".
Something like the below; untested of course. But I guess there must be
some arch specific vcpu flags, which can be used to achieve the same?
diff --git a/arch/s390/include/asm/thread_info.h b/arch/s390/include/asm/thread_info.h
index a674c7d25da5..b9ff8b125fb8 100644
--- a/arch/s390/include/asm/thread_info.h
+++ b/arch/s390/include/asm/thread_info.h
@@ -69,6 +69,7 @@ void arch_setup_new_exec(void);
#define TIF_PATCH_PENDING 5 /* pending live patching update */
#define TIF_PGSTE 6 /* New mm's will use 4K page tables */
#define TIF_NOTIFY_SIGNAL 7 /* signal notifications exist */
+#define TIF_KVM_ACRS 8 /* access registers contain guest content */
#define TIF_ISOLATE_BP_GUEST 9 /* Run KVM guests with isolated BP */
#define TIF_PER_TRAP 10 /* Need to handle PER trap on exit to usermode */
diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
index 5bfcc50c1a68..b0ef242d2371 100644
--- a/arch/s390/kvm/gaccess.c
+++ b/arch/s390/kvm/gaccess.c
@@ -391,7 +391,8 @@ static int ar_translation(struct kvm_vcpu *vcpu, union asce *asce, u8 ar,
if (ar >= NUM_ACRS)
return -EINVAL;
- save_access_regs(vcpu->run->s.regs.acrs);
+ if (test_thread_flag(TIF_KVM_ACRS))
+ save_access_regs(vcpu->run->s.regs.acrs);
alet.val = vcpu->run->s.regs.acrs[ar];
if (ar == 0 || alet.val == 0) {
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index ea63ac769889..3ee0913639d5 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -4951,6 +4951,7 @@ static void sync_regs(struct kvm_vcpu *vcpu)
}
save_access_regs(vcpu->arch.host_acrs);
restore_access_regs(vcpu->run->s.regs.acrs);
+ set_thread_flag(TIF_KVM_ACRS);
/* save host (userspace) fprs/vrs */
save_fpu_regs();
vcpu->arch.host_fpregs.fpc = current->thread.fpu.fpc;
@@ -5020,6 +5021,7 @@ static void store_regs(struct kvm_vcpu *vcpu)
kvm_run->s.regs.pfs = vcpu->arch.pfault_select;
kvm_run->s.regs.pfc = vcpu->arch.pfault_compare;
save_access_regs(vcpu->run->s.regs.acrs);
+ clear_thread_flag(TIF_KVM_ACRS);
restore_access_regs(vcpu->arch.host_acrs);
/* Save guest register state */
save_fpu_regs();
