From 528ada2811ba0bb2b2db5bf0f829b48c50f3c13c Mon Sep 17 00:00:00 2001 From: Marc Zyngier Date: Mon, 16 May 2022 17:32:54 +0100 Subject: [PATCH] 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: 05714cab7d63 ("KVM: arm64: Setup a framework for hypercall bitmap firmware registers") Signed-off-by: Marc Zyngier --- arch/arm64/kvm/hypercalls.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c index ccbd3ce..c9f401f 100644 --- a/arch/arm64/kvm/hypercalls.c +++ b/arch/arm64/kvm/hypercalls.c @@ -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; } -- 2.7.4