linux-kernel - Re: [Part1 PATCH v7 13/17] x86/io: Unroll string I/O when SEV is active

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Message-ID: <e98c9c16-0dfd-708f-64c7-764fd50d46e3@amd.com>
Date:   Sat, 21 Oct 2017 06:26:52 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Alan Cox <gnomes@...rguk.ukuu.org.uk>
Cc:     brijesh.singh@....com, x86@...nel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...e.de>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        David Laight <David.Laight@...LAB.COM>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [Part1 PATCH v7 13/17] x86/io: Unroll string I/O when SEV is
 active

Hi Alan,


On 10/20/17 1:39 PM, Alan Cox wrote:
> On Fri, 20 Oct 2017 09:30:55 -0500
> Brijesh Singh <brijesh.singh@....com> wrote:
>
>> From: Tom Lendacky <thomas.lendacky@....com>
>>
>> Secure Encrypted Virtualization (SEV) does not support string I/O, so
>> unroll the string I/O operation into a loop operating on one element at
>> a time.
> Does this also mean that any firmware running in the virtual machine
> (EFI, BIOS, VGA etc) has to be patched and if so shouldn't that be
> documented somewhere ?

Yes. SEV support has been added to EDK2/OVMF virtual machine bios and we
have similar patch [1].

[1]
https://github.com/tianocore/edk2/commit/b6d11d7c467810ea7f2e2eda46ef0bdc57bf1475

-Brijesh