linux-kernel - Re: [PATCH v2 03/12] x86/sev: Add an x86 version of prot_guest

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Date:   Thu, 19 Aug 2021 13:33:09 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     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>,
        Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...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>,
        Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH v2 03/12] x86/sev: Add an x86 version of prot_guest_has()

On 8/19/21 4:52 AM, Christoph Hellwig wrote:
> On Fri, Aug 13, 2021 at 11:59:22AM -0500, Tom Lendacky wrote:
>> While the name suggests this is intended mainly for guests, it will
>> also be used for host memory encryption checks in place of sme_active().
> 
> Which suggest that the name is not good to start with.  Maybe protected
> hardware, system or platform might be a better choice?
> 
>> +static inline bool prot_guest_has(unsigned int attr)
>> +{
>> +#ifdef CONFIG_AMD_MEM_ENCRYPT
>> +	if (sme_me_mask)
>> +		return amd_prot_guest_has(attr);
>> +#endif
>> +
>> +	return false;
>> +}
> 
> Shouldn't this be entirely out of line?

I did it as inline originally because the presence of the function will be
decided based on the ARCH_HAS_PROTECTED_GUEST config. For now, that is
only selected by the AMD memory encryption support, so if I went out of
line I could put in mem_encrypt.c. But with TDX wanting to also use it, it
would have to be in an always built file with some #ifdefs or in its own
file that is conditionally built based on the ARCH_HAS_PROTECTED_GUEST
setting (they've already tried building with ARCH_HAS_PROTECTED_GUEST=y
and AMD_MEM_ENCRYPT not set).

To take it out of line, I'm leaning towards the latter, creating a new
file that is built based on the ARCH_HAS_PROTECTED_GUEST setting.

> 
>> +/* 0x800 - 0x8ff reserved for AMD */
>> +#define PATTR_SME			0x800
>> +#define PATTR_SEV			0x801
>> +#define PATTR_SEV_ES			0x802
> 
> Why do we need reservations for a purely in-kernel namespace?
> 
> And why are you overoading a brand new generic API with weird details
> of a specific implementation like this?

There was some talk about this on the mailing list where TDX and SEV may
need to be differentiated, so we wanted to reserve a range of values per
technology. I guess I can remove them until they are actually needed.

Thanks,
Tom

>