linux-kernel - [PATCH stable-5.12.y backport 2/2] KVM: arm64: Resolve all pending PC updates before immediate exit

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Date:   Tue, 1 Jun 2021 19:12:38 +0800
From:   Zenghui Yu <yuzenghui@...wei.com>
To:     <stable@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     <gregkh@...uxfoundation.org>, <sashal@...nel.org>,
        <maz@...nel.org>, <alexandru.elisei@....com>,
        <wanghaibin.wang@...wei.com>, <yuzenghui@...wei.com>
Subject: [PATCH stable-5.12.y backport 2/2] KVM: arm64: Resolve all pending PC updates before immediate exit

commit e3e880bb1518eb10a4b4bb4344ed614d6856f190 upstream.

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).

Fixes: 26778aaa134a ("KVM: arm64: Commit pending PC adjustemnts before returning to userspace")
Signed-off-by: Zenghui Yu <yuzenghui@...wei.com>
Signed-off-by: Marc Zyngier <maz@...nel.org>
Link: https://lore.kernel.org/r/20210526141831.1662-1-yuzenghui@huawei.com
Cc: stable@...r.kernel.org # 5.11
---
 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 c18740a1e541..7730b81aad6d 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -715,11 +715,13 @@ 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;
@@ -892,6 +894,7 @@ 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