Re: [PATCH 3/4] KVM: x86: WARN and reject loading KVM if NX is supported but not enabled
From: Sean Christopherson
Date: Thu Jun 24 2021 - 18:33:57 EST
On Tue, Jun 15, 2021, Sean Christopherson wrote:
> WARN if NX is reported as supported but not enabled in EFER. All flavors
> of the kernel, including non-PAE 32-bit kernels, set EFER.NX=1 if NX is
> supported, even if NX usage is disable via kernel command line.
Ugh, I misread .Ldefault_entry in head_32.S, it skips over the entire EFER code
if PAE=0. Apparently I didn't test this with non-PAE paging and EPT?
Paolo, I'll send a revert since it's in kvm/next, but even better would be if
you can drop the patch :-) Lucky for me you didn't pick up patch 4/4 that
depends on this...
I'll revisit this mess in a few weeks.
> on NX being enabled if it's supported, e.g. KVM will generate illegal NPT
> entries if nx_huge_pages is enabled and NX is supported but not enabled.
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> arch/x86/kvm/x86.c | 3 +++
> 1 file changed, 3 insertions(+)
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index acc28473dec7..1f6595df45de 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10981,6 +10981,9 @@ int kvm_arch_hardware_setup(void *opaque)
> int r;
> rdmsrl_safe(MSR_EFER, &host_efer);
> + if (WARN_ON_ONCE(boot_cpu_has(X86_FEATURE_NX) &&
> + !(host_efer & EFER_NX)))
> + return -EIO;
> if (boot_cpu_has(X86_FEATURE_XSAVES))
> rdmsrl(MSR_IA32_XSS, host_xss);