From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Revert "KVM: x86: WARN and reject loading KVM if NX is supported but not enabled"
Date: Thu, 8 Jul 2021 18:17:59 +0200 [thread overview]
Message-ID: <28ec9d07-756b-f546-dad1-0af751167838@redhat.com> (raw)
In-Reply-To: <20210625001853.318148-1-seanjc@google.com>
On 25/06/21 02:18, Sean Christopherson wrote:
> Let KVM load if EFER.NX=0 even if NX is supported, the analysis and
> testing (or lack thereof) for the non-PAE host case was garbage.
>
> If the kernel won't be using PAE paging, .Ldefault_entry in head_32.S
> skips over the entire EFER sequence. Hopefully that can be changed in
> the future to allow KVM to require EFER.NX, but the motivation behind
> KVM's requirement isn't yet merged. Reverting and revisiting the mess
> at a later date is by far the safest approach.
>
> This reverts commit 8bbed95d2cb6e5de8a342d761a89b0a04faed7be.
>
> Fixes: 8bbed95d2cb6 ("KVM: x86: WARN and reject loading KVM if NX is supported but not enabled")
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>
> Hopefully it's not too late to just drop the original patch...
>
> arch/x86/kvm/x86.c | 3 ---
> 1 file changed, 3 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 4a597aafe637..1cc02a3685d0 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10981,9 +10981,6 @@ 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);
>
So do we want this or "depends on X86_64 || X86_PAE"?
Paolo
next prev parent reply other threads:[~2021-07-08 16:18 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-25 0:18 [PATCH] Revert "KVM: x86: WARN and reject loading KVM if NX is supported but not enabled" Sean Christopherson
2021-07-08 16:17 ` Paolo Bonzini [this message]
2021-07-09 17:21 ` Sean Christopherson
2021-07-09 17:32 ` Paolo Bonzini
2021-07-12 7:52 ` Yu Zhang
2021-07-12 14:36 ` Sean Christopherson
2021-07-13 3:59 ` Yu Zhang
2021-07-21 21:28 ` Sean Christopherson
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