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[213.175.37.10]) by smtp.gmail.com with ESMTPSA id m11sm1461332wrn.92.2020.03.06.02.15.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Mar 2020 02:15:21 -0800 (PST) From: Vitaly Kuznetsov To: Paolo Bonzini , linmiaohe Cc: "rkrcmar\@redhat.com" , "sean.j.christopherson\@intel.com" , "jmattson\@google.com" , "joro\@8bytes.org" , "tglx\@linutronix.de" , "mingo\@redhat.com" , "bp\@alien8.de" , "hpa\@zytor.com" , "kvm\@vger.kernel.org" , "linux-kernel\@vger.kernel.org" , "x86\@kernel.org" Subject: Re: [PATCH] KVM: VMX: Use wrapper macro ~RMODE_GUEST_OWNED_EFLAGS_BITS directly In-Reply-To: <2cde5e91-b357-81f9-9e39-fd5d99bb81fd@redhat.com> References: <1e3f7ff0-0159-98e8-ba21-8806c3a14820@redhat.com> <87sgiles16.fsf@vitty.brq.redhat.com> <2cde5e91-b357-81f9-9e39-fd5d99bb81fd@redhat.com> Date: Fri, 06 Mar 2020 11:15:20 +0100 Message-ID: <87lfodeqmf.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Paolo Bonzini writes: > On 06/03/20 10:44, Vitaly Kuznetsov wrote: >>>> Define a macro RMODE_HOST_OWNED_EFLAGS_BITS for (X86_EFLAGS_IOPL | >>>> X86_EFLAGS_VM) as suggested by Vitaly seems a good way to fix this ? >>>> Thanks. >>> No, what if a host-owned flag was zero? I'd just leave it as is. >>> >> I'm not saying my suggestion was a good idea but honestly I'm failing to >> wrap my head around this. The suggested 'RMODE_HOST_OWNED_EFLAGS_BITS' >> would just be a define for (X86_EFLAGS_IOPL | X86_EFLAGS_VM) so >> technically the patch would just be nop, no? > > It would not be a nop for the reader. > > Something called RMODE_{GUEST,HOST}_OWNED_EFLAGS_BITS is a mask. It > tells you nothing about whether those bugs are 0 or 1. It's just by > chance that all three host-owned EFLAGS bits are 1 while in real mode. > It wouldn't be the case if, for example, we ran the guest using vm86 > mode extensions (i.e. setting CR4.VME=1). Then VIF would be host-owned, > but it wouldn't necessarily be 1. Got it, it's the name which is causing the confusion, we're using mask as something different. Make sense, let's keep the code as-is then. -- Vitaly