linux-kernel - Re: [PATCH v5 06/14] x86/ioremap: Support hypervisor specified range to map as encrypted

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Message-ID: <a4fc8686-f82d-370e-309f-d6d3fc0568e8@amd.com>
Date:   Thu, 9 Mar 2023 08:19:58 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Borislav Petkov <bp@...en8.de>,
        David Woodhouse <dwmw2@...radead.org>,
        Jörg Rödel <joro@...tes.org>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        Sean Christopherson <seanjc@...gle.com>,
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        Dexuan Cui <decui@...rosoft.com>,
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Subject: Re: [PATCH v5 06/14] x86/ioremap: Support hypervisor specified range
 to map as encrypted

On 3/9/23 05:59, Borislav Petkov wrote:
> First of all,
> 
> thanks for proactively pointing that out instead of simply using what's
> there and we get to find out later, only by chance.
> 
> Much appreciated. :-)
> 
> On Thu, Mar 09, 2023 at 11:12:10AM +0000, David Woodhouse wrote:
>>> Right, I think we're ok with the following basic rules:
>>>
>>> - pure arch/x86/ code should use the x86_platform function pointers to
>>>    query hypervisor capabilities/peculiarities
>>>
>>> - cc_platform_has() should be used in generic/driver code as it
>>>    abstracts away the underlying platform better. IOW, querying
>>>    x86_platform.... in generic, platform-agnostic driver code looks weird to
>>>    say the least
>>>
>>> The hope is that those two should be enough to support most guest types
>>> and not let the zoo get too much out of hand...
>>>
>>> Thx.
>>
>> In
>> https://lore.kernel.org/all/20230308171328.1562857-13-usama.arif@bytedance.com/
>> I added an sev_es_active() helper for x86 code.
>>
>> Is that consistent with the vision here, or should I do something different?
> 
> So looking at sev_es_init_vc_handling() where we set that key, I'm
> *thinking* that key can be removed now and the code should check
> 
>    cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT)
> 
> instead.
> 
> Because if some of the checks in that function below fail, the guest
> will terminate anyway.
> 
> Jörg, Tom?

I believe Joerg added that key for performance reasons, since it is used 
on the exception path and can avoid all the calls to cc_platform_has(). I 
think that key should stay.

Maybe David can introduce an CC_ATTR_GUEST_SEV_ES attribute that returns 
true if the guest is an ES or SNP guest. Or do we introduce a 
CC_ATTR_PARALLEL_BOOT attribute that returns true for any SEV guest.

Then the "if cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT) && !has_sev_es" 
check in arch/x86/kernel/smpboot.c can be removed and the following check 
can become if (x2apic_mode || cc_platform_has(CC_ATTR_PARALLEL_BOOT))

Not sure how that affects a TDX guest, though.

Thanks,
Tom

>