Re: [PATCH v2 1/3] KVM: x86: dump_vmcs should not assume GUEST_IA32_EFER is valid

Sean Christopherson
2021-02-23T23:01:33Z

On Fri, Feb 19, 2021, David Edmondson wrote:
> If the VM entry/exit controls for loading/saving MSR_EFER are either
> not available (an older processor or explicitly disabled) or not
> used (host and guest values are the same), reading GUEST_IA32_EFER
> from the VMCS returns an inaccurate value.
>
> Because of this, in dump_vmcs() don't use GUEST_IA32_EFER to decide
> whether to print the PDPTRs - do so if the EPT is in use and CR4.PAE
> is set.

This isn't necessarily correct either. In a way, it's less correct as PDPTRs
are more likely to be printed when they shouldn't, assuming most guests are
64-bit guests. It's annoying to calculate the effective guest EFER, but so
awful that it's worth risking confusion over PDTPRs.

> Fixes: 4eb64dce8d0a ("KVM: x86: dump VMCS on invalid entry")
> Signed-off-by: David Edmondson <david.edmondson@oracle.com>
> ---
> arch/x86/kvm/vmx/vmx.c | 8 +++-----
> 1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index eb69fef57485..818051c9fa10 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -5759,7 +5759,6 @@ void dump_vmcs(void)
> u32 vmentry_ctl, vmexit_ctl;
> u32 cpu_based_exec_ctrl, pin_based_exec_ctrl, secondary_exec_control;
> unsigned long cr4;
> - u64 efer;
>
> if (!dump_invalid_vmcs) {
> pr_warn_ratelimited("set kvm_intel.dump_invalid_vmcs=1 to dump internal KVM state.\n");
> @@ -5771,7 +5770,6 @@ void dump_vmcs(void)
> cpu_based_exec_ctrl = vmcs_read32(CPU_BASED_VM_EXEC_CONTROL);
> pin_based_exec_ctrl = vmcs_read32(PIN_BASED_VM_EXEC_CONTROL);
> cr4 = vmcs_readl(GUEST_CR4);
> - efer = vmcs_read64(GUEST_IA32_EFER);
> secondary_exec_control = 0;
> if (cpu_has_secondary_exec_ctrls())
> secondary_exec_control = vmcs_read32(SECONDARY_VM_EXEC_CONTROL);
> @@ -5784,8 +5782,7 @@ void dump_vmcs(void)
> cr4, vmcs_readl(CR4_READ_SHADOW), vmcs_readl(CR4_GUEST_HOST_MASK));
> pr_err("CR3 = 0x%016lx\n", vmcs_readl(GUEST_CR3));
> if ((secondary_exec_control & SECONDARY_EXEC_ENABLE_EPT) &&
> - (cr4 & X86_CR4_PAE) && !(efer & EFER_LMA))
> - {
> + (cr4 & X86_CR4_PAE)) {
> pr_err("PDPTR0 = 0x%016llx PDPTR1 = 0x%016llx\n",
> vmcs_read64(GUEST_PDPTR0), vmcs_read64(GUEST_PDPTR1));
> pr_err("PDPTR2 = 0x%016llx PDPTR3 = 0x%016llx\n",
> @@ -5811,7 +5808,8 @@ void dump_vmcs(void)
> if ((vmexit_ctl & (VM_EXIT_SAVE_IA32_PAT | VM_EXIT_SAVE_IA32_EFER)) ||
> (vmentry_ctl & (VM_ENTRY_LOAD_IA32_PAT | VM_ENTRY_LOAD_IA32_EFER)))
> pr_err("EFER = 0x%016llx PAT = 0x%016llx\n",
> - efer, vmcs_read64(GUEST_IA32_PAT));
> + vmcs_read64(GUEST_IA32_EFER),
> + vmcs_read64(GUEST_IA32_PAT));
> pr_err("DebugCtl = 0x%016llx DebugExceptions = 0x%016lx\n",
> vmcs_read64(GUEST_IA32_DEBUGCTL),
> vmcs_readl(GUEST_PENDING_DBG_EXCEPTIONS));
> --
> 2.30.0
>