On 2021/12/15 23:47, Maxim Levitsky wrote:
On Mon, 2021-11-08 at 20:44 +0800, Lai Jiangshan wrote:
From: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
When vcpu->arch.cr3 is changed, it is marked dirty, so vmcs.GUEST_CR3
can be updated only when kvm_register_is_dirty(vcpu, VCPU_EXREG_CR3).
Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
---
arch/x86/kvm/vmx/vmx.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index d94e51e9c08f..38b65b97fb7b 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3126,9 +3126,9 @@ static void vmx_load_mmu_pgd(struct kvm_vcpu *vcpu, hpa_t root_hpa,
if (!enable_unrestricted_guest && !is_paging(vcpu))
guest_cr3 = to_kvm_vmx(kvm)->ept_identity_map_addr;
- else if (test_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail))
+ else if (kvm_register_is_dirty(vcpu, VCPU_EXREG_CR3))
guest_cr3 = vcpu->arch.cr3;
- else /* vmcs01.GUEST_CR3 is already up-to-date. */
+ else /* vmcs.GUEST_CR3 is already up-to-date. */
update_guest_cr3 = false;
vmx_ept_load_pdptrs(vcpu);
} else {
I just bisected this patch to break booting a VM with ept=1 but unrestricted_guest=0
(I needed to re-test unrestricted_guest=0 bug related to SMM, but didn't want
to boot without EPT. With ept=0,the VM boots with this patch applied).
Thanks for reporting.
Sorry, I never tested it with unrestricted_guest=0. I can't reproduce it now shortly
with unrestricted_guest=0. Maybe it can be reproduced easily if I try more guests or
I write a piece of guest code to deliberate hit it if the following analyses is correct.
All the paths changing %cr3 are followed with kvm_register_mark_dirty(vcpu, VCPU_EXREG_CR3)
and GUEST_CR3 will be expected to be updated.
What I missed is the case of "if (!enable_unrestricted_guest && !is_paging(vcpu))"
in vmx_load_mmu_pgd() which doesn't load GUEST_CR3 but clears dirty of VCPU_EXREG_CR3
(when after next run).
So when CR0 !PG -> PG, VCPU_EXREG_CR3 dirty bit should be set.
Maybe adding the following patch on top of the original patch can work.
Thanks
Lai
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 85127b3e3690..55b45005ebb9 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -858,6 +858,7 @@ void kvm_post_set_cr0(struct kvm_vcpu *vcpu, unsigned long old_cr0, unsigned lon
if ((cr0 ^ old_cr0) & X86_CR0_PG) {
kvm_clear_async_pf_completion_queue(vcpu);
kvm_async_pf_hash_reset(vcpu);
+ kvm_register_mark_dirty(vcpu, VCPU_EXREG_CR3);
}
if ((cr0 ^ old_cr0) & KVM_MMU_CR0_ROLE_BITS)
