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UPSTREAM: KVM: arm64: Fix hypercall bitmap writeback when vcpus have already run

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We generally want to disallow hypercall bitmaps being changed
once vcpus have already run. But we must allow the write if
the written value is unchanged so that userspace can rewrite
the register file on reboot, for example.

Without this, a QEMU-based VM will fail to reboot correctly.

The original code was correct, and it is me that introduced
the regression.

Fixes: 05714cab7d ("KVM: arm64: Setup a framework for hypercall bitmap firmware registers")
Signed-off-by: Marc Zyngier <maz@kernel.org>
(cherry picked from commit 528ada2811)
Signed-off-by: Will Deacon <willdeacon@google.com>
Bug: 233587962
Bug: 233588291
Change-Id: Ic7ab0c0c23762150b2970fd0bdfe7c1612f1f394
This commit is contained in:
Marc Zyngier
2022-05-16 17:32:54 +01:00
committed by Will Deacon
parent 6038bcf891
commit fa90e30438
1 changed files with 2 additions and 1 deletions
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3
arch/arm64/kvm/hypercalls.c
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@@ -379,7 +379,8 @@ static int kvm_arm_set_fw_reg_bmap(struct kvm_vcpu *vcpu, u64 reg_id, u64 val)
mutex_lock(&kvm->lock);
if (test_bit(KVM_ARCH_FLAG_HAS_RAN_ONCE, &kvm->arch.flags)) {
if (test_bit(KVM_ARCH_FLAG_HAS_RAN_ONCE, &kvm->arch.flags) &&
val != *fw_reg_bmap) {
ret = -EBUSY;
goto out;
}