From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>, linmiaohe <linmiaohe@huawei.com>
Cc: "rkrcmar\@redhat.com" <rkrcmar@redhat.com>,
"sean.j.christopherson\@intel.com"
<sean.j.christopherson@intel.com>,
"jmattson\@google.com" <jmattson@google.com>,
"joro\@8bytes.org" <joro@8bytes.org>,
"tglx\@linutronix.de" <tglx@linutronix.de>,
"mingo\@redhat.com" <mingo@redhat.com>,
"bp\@alien8.de" <bp@alien8.de>, "hpa\@zytor.com" <hpa@zytor.com>,
"kvm\@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"x86\@kernel.org" <x86@kernel.org>
Subject: Re: [PATCH] KVM: VMX: Use wrapper macro ~RMODE_GUEST_OWNED_EFLAGS_BITS directly
Date: Fri, 06 Mar 2020 11:15:20 +0100 [thread overview]
Message-ID: <87lfodeqmf.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <2cde5e91-b357-81f9-9e39-fd5d99bb81fd@redhat.com>
Paolo Bonzini <pbonzini@redhat.com> 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
next prev parent reply other threads:[~2020-03-06 10:15 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-06 2:17 [PATCH] KVM: VMX: Use wrapper macro ~RMODE_GUEST_OWNED_EFLAGS_BITS directly linmiaohe
2020-03-06 5:32 ` Paolo Bonzini
2020-03-06 9:44 ` Vitaly Kuznetsov
2020-03-06 10:00 ` Paolo Bonzini
2020-03-06 10:15 ` Vitaly Kuznetsov [this message]
-- strict thread matches above, loose matches on Subject: below --
2020-03-06 2:11 linmiaohe
2020-03-05 2:35 linmiaohe
2020-03-05 10:08 ` Vitaly Kuznetsov
2020-03-05 11:49 ` Paolo Bonzini
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