linux-kernel - Re: [PATCH] Allow RDTSC and RDTSCP from userspace

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Message-ID: <ead88d04-1756-1190-2b37-b24f86422595@amd.com>
Date:   Fri, 24 Apr 2020 16:27:32 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Mike Stunes <mstunes@...are.com>, joro@...tes.org
Cc:     dan.j.williams@...el.com, dave.hansen@...ux.intel.com,
        hpa@...or.com, jgross@...e.com, jroedel@...e.de, jslaby@...e.cz,
        keescook@...omium.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, luto@...nel.org,
        peterz@...radead.org, thellstrom@...are.com,
        virtualization@...ts.linux-foundation.org, x86@...nel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [PATCH] Allow RDTSC and RDTSCP from userspace

On 4/24/20 4:24 PM, Dave Hansen wrote:
> On 4/24/20 2:03 PM, Mike Stunes wrote:
>> I needed to allow RDTSC(P) from userspace and in early boot in order to
>> get userspace started properly. Patch below.
>>
>> ---
>> SEV-ES guests will need to execute rdtsc and rdtscp from userspace and
>> during early boot. Move the rdtsc(p) #VC handler into common code and
>> extend the #VC handlers.
> 
> Do SEV-ES guests _always_ #VC on rdtsc(p)?

Only if the hypervisor is intercepting those instructions.

Thanks,
Tom

>