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

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>
This commit is contained in:
Marc Zyngier 2022-05-16 17:32:54 +01:00
parent 2cde51f1e1
commit 528ada2811
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;
}