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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id ja11sm1182528ejc.62.2021.07.08.09.18.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 08 Jul 2021 09:18:01 -0700 (PDT) Subject: Re: [PATCH] Revert "KVM: x86: WARN and reject loading KVM if NX is supported but not enabled" To: Sean Christopherson Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210625001853.318148-1-seanjc@google.com> From: Paolo Bonzini Message-ID: <28ec9d07-756b-f546-dad1-0af751167838@redhat.com> Date: Thu, 8 Jul 2021 18:17:59 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210625001853.318148-1-seanjc@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > --- > > 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