linux-kernel - Re: [PATCH 07/11] treewide: Replace the use of mem_encrypt_active() with prot_guest

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Date:   Fri, 13 Aug 2021 12:08:59 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        iommu@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-graphics-maintainer@...are.com,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        kexec@...ts.infradead.org, linux-fsdevel@...r.kernel.org,
        Borislav Petkov <bp@...en8.de>,
        Brijesh Singh <brijesh.singh@....com>,
        Joerg Roedel <joro@...tes.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Will Deacon <will@...nel.org>, Dave Young <dyoung@...hat.com>,
        Baoquan He <bhe@...hat.com>
Subject: Re: [PATCH 07/11] treewide: Replace the use of mem_encrypt_active()
 with prot_guest_has()

On 8/12/21 5:07 AM, Kirill A. Shutemov wrote:
> On Wed, Aug 11, 2021 at 10:52:55AM -0500, Tom Lendacky wrote:
>> On 8/11/21 7:19 AM, Kirill A. Shutemov wrote:
>>> On Tue, Aug 10, 2021 at 02:48:54PM -0500, Tom Lendacky wrote:
>>>> On 8/10/21 1:45 PM, Kuppuswamy, Sathyanarayanan wrote:
...
>>> Looking at code agains, now I *think* the reason is accessing a global
>>> variable from __startup_64() inside TDX version of prot_guest_has().
>>>
>>> __startup_64() is special. If you access any global variable you need to
>>> use fixup_pointer(). See comment before __startup_64().
>>>
>>> I'm not sure how you get away with accessing sme_me_mask directly from
>>> there. Any clues? Maybe just a luck and complier generates code just right
>>> for your case, I donno.
>>
>> Hmm... yeah, could be that the compiler is using rip-relative addressing
>> for it because it lives in the .data section?
> 
> I guess. It has to be fixed. It may break with complier upgrade or any
> random change around the code.

I'll look at doing that separate from this series.

> 
> BTW, does it work with clang for you?

I haven't tried with clang, I'll check on that.

Thanks,
Tom

>