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From:   Andy Lutomirski <luto@amacapital.net>
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Subject: Re: [PATCH v3 1/1] x86/tdx: Handle MWAIT, MONITOR and WBINVD
Date:   Tue, 30 Mar 2021 09:37:30 -0700
Message-Id: <4DD05B91-13B3-4842-A215-C8DC6F34F219@amacapital.net>
References: <YGNAQrWMl3AZQ3HG@google.com>
Cc:     Andi Kleen <ak@linux.intel.com>, Andy Lutomirski <luto@kernel.org>,
        "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Kirill Shutemov <kirill.shutemov@linux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Raj Ashok <ashok.raj@intel.com>,
        LKML <linux-kernel@vger.kernel.org>
In-Reply-To: <YGNAQrWMl3AZQ3HG@google.com>
To:     Sean Christopherson <seanjc@google.com>
Precedence: bulk


> On Mar 30, 2021, at 8:14 AM, Sean Christopherson <seanjc@google.com> wrote=
:
>=20
> =EF=BB=BFOn Mon, Mar 29, 2021, Andy Lutomirski wrote:
>>=20
>>>> On Mar 29, 2021, at 7:04 PM, Andi Kleen <ak@linux.intel.com> wrote:
>>>=20
>>> =EF=BB=BF
>>>>=20
>>>>> No, if these instructions take a #VE then they were executed at CPL=3D=
0.  MONITOR
>>>>> and MWAIT will #UD without VM-Exit->#VE.  Same for WBINVD, s/#UD/#GP.
>>>>=20
>>>> Dare I ask about XSETBV?
>>>=20
>>> XGETBV does not cause a #VE, it just works normally. The guest has full
>>> AVX capabilities.
>>>=20
>>=20
>> X *SET* BV
>=20
> Heh, XSETBV also works normally, relative to the features enumerated in CP=
UID.
> XSAVES/XRSTORS support is fixed to '1' in the virtual CPU model.  A subset=
 of
> the features managed by XSAVE can be hidden by the VMM, but attempting to e=
nable
> unsupported features will #GP (either from hardware or injected by TDX Mod=
ule),
> not #VE.

Normally in non-root mode means that every XSETBV results in a VM exit and, I=
IUC, there=E2=80=99s a buglet in that this happens even if CPL=3D=3D3.  Does=
 something special happen in TDX or does the exit get reflected back to the g=
uest as a #VE?=