2021-05-26 22:04:16

by Zenghui Yu

Subject: [PATCH] KVM: arm64: Resolve all pending PC updates before immediate exit

Commit 26778aaa134a ("KVM: arm64: Commit pending PC adjustemnts before
returning to userspace") fixed the PC updating issue by forcing an explicit
synchronisation of the exception state on vcpu exit to userspace.

However, we forgot to take into account the case where immediate_exit is
set by userspace and KVM_RUN will exit immediately. Fix it by resolving all
pending PC updates before returning to userspace.

Since __kvm_adjust_pc() relies on a loaded vcpu context, I moved the
immediate_exit checking right after vcpu_load(). We will get some overhead
if immediate_exit is true (which should hopefully be rare).

Signed-off-by: Zenghui Yu <[email protected]>
---

This patch can be applied on top of kvmarm/fixes and help me to PASS all
kvm-unit-tests cases in the migration group.

arch/arm64/kvm/arm.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 1126eae27400..e720148232a0 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -720,11 +720,13 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
return ret;
}

- if (run->immediate_exit)
- return -EINTR;
-
vcpu_load(vcpu);

+ if (run->immediate_exit) {
+ ret = -EINTR;
+ goto out;
+ }
+
kvm_sigset_activate(vcpu);

ret = 1;
@@ -897,6 +899,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)

kvm_sigset_deactivate(vcpu);

+out:
/*
* In the unlikely event that we are returning to userspace
* with pending exceptions or PC adjustment, commit these
--
2.19.1

2021-05-27 09:40:48

by Marc Zyngier

Subject: Re: [PATCH] KVM: arm64: Resolve all pending PC updates before immediate exit

On Wed, 26 May 2021 22:18:31 +0800, Zenghui Yu wrote:
> Commit 26778aaa134a ("KVM: arm64: Commit pending PC adjustemnts before
> returning to userspace") fixed the PC updating issue by forcing an explicit
> synchronisation of the exception state on vcpu exit to userspace.
>
> However, we forgot to take into account the case where immediate_exit is
> set by userspace and KVM_RUN will exit immediately. Fix it by resolving all
> pending PC updates before returning to userspace.
>
> [...]

Applied to fixes, thanks!

[1/1] KVM: arm64: Resolve all pending PC updates before immediate exit
commit: e3e880bb1518eb10a4b4bb4344ed614d6856f190

with:
Fixes: 26778aaa134a ("KVM: arm64: Commit pending PC adjustemnts before returning to userspace")
Cc: [email protected] # 5.11

Cheers,

M.
--
Without deviation from the norm, progress is not possible.