Re: [PATCH v2 03/12] x86/sev: Add an x86 version of prot_guest_has()

Tom Lendacky
2021-08-19T18:33:20Z

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

>