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SubjectRe: [PATCH 1/4] KVM: X86: Fix tlb flush for tdp in kvm_invalidate_pcid()
On Wed, Oct 20, 2021, Lai Jiangshan wrote:
> On 2021/10/19 23:25, Sean Christopherson wrote:
> I just read some interception policy in vmx.c, if EPT=1 but vmx_need_pf_intercept()
> return true for some reasons/configs, #PF is intercepted. But CR3 write is not
> intercepted, which means there will be an EPT fault _after_ (IIUC) the CR3 write if
> the GPA of the new CR3 exceeds the guest maxphyaddr limit. And kvm queues a fault to
> the guest which is also _after_ the CR3 write, but the guest expects the fault before
> the write.
> IIUC, it can be fixed by intercepting CR3 write or reversing the CR3 write in EPT
> violation handler.

KVM implicitly does the latter by emulating the faulting instruction.

static int handle_ept_violation(struct kvm_vcpu *vcpu)

* Check that the GPA doesn't exceed physical memory limits, as that is
* a guest page fault. We have to emulate the instruction here, because
* if the illegal address is that of a paging structure, then
* EPT_VIOLATION_ACC_WRITE bit is set. Alternatively, if supported we
* would also use advanced VM-exit information for EPT violations to
* reconstruct the page fault error code.
if (unlikely(allow_smaller_maxphyaddr && kvm_vcpu_is_illegal_gpa(vcpu, gpa)))
return kvm_emulate_instruction(vcpu, 0);

return kvm_mmu_page_fault(vcpu, gpa, error_code, NULL, 0);

and injecting a #GP when kvm_set_cr3() fails.

static int em_cr_write(struct x86_emulate_ctxt *ctxt)
if (ctxt->ops->set_cr(ctxt, ctxt->modrm_reg, ctxt->src.val))
return emulate_gp(ctxt, 0);

/* Disable writeback. */
ctxt->dst.type = OP_NONE;

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