Re: [Xen-devel] [PATCH v7 08/36] x86/mm: Add support to enable SME in early boot processing

[Tom Lendacky <thomas.lendacky@xxxxxxx>]

On 6/21/2017 10:38 AM, Thomas Gleixner wrote:
> On Wed, 21 Jun 2017, Tom Lendacky wrote:
> > On 6/21/2017 2:16 AM, Thomas Gleixner wrote:
> > > Why is this an unconditional function? Isn't the mask simply 0 when the MEM
> > > ENCRYPT support is disabled?
> > I made it unconditional because of the call from head_64.S. I can't make
> > use of the C level static inline function and since the mask is not a
> > variable if CONFIG_AMD_MEM_ENCRYPT is not configured (#defined to 0) I
> > can't reference the variable directly.
> >
> > I could create a #define in head_64.S that changes this to load rax with
> > the variable if CONFIG_AMD_MEM_ENCRYPT is configured or a zero if it's
> > not or add a #ifdef at that point in the code directly. Thoughts on
> > that?
> See below.
>
> > > That does not make any sense. Neither the call to sme_encrypt_kernel() nor
> > > the following call to sme_get_me_mask().
> > >
> > > __startup_64() is already C code, so why can't you simply call that from
> > > __startup_64() in C and return the mask from there?
> > I was trying to keep it explicit as to what was happening, but I can
> > move those calls into __startup_64().
> That's much preferred. And the return value wants to be documented in both
> C and ASM code.
Will do.

> > I'll still need the call to sme_get_me_mask() in the secondary_startup_64
> > path, though (depending on your thoughts to the above response).
>          call verify_cpu
>
>          movq    $(init_top_pgt - __START_KERNEL_map), %rax
>
> So if you make that:
>
>         /*
>          * Sanitize CPU configuration and retrieve the modifier
>          * for the initial pgdir entry which will be programmed
>          * into CR3. Depends on enabled SME encryption, normally 0.
>          */
>         call __startup_secondary_64
>
>          addq    $(init_top_pgt - __START_KERNEL_map), %rax
>
> You can hide that stuff in C-code nicely without adding any cruft to the
> ASM code.
Moving the call to verify_cpu into the C-code might be quite a bit of
change.  Currently, the verify_cpu code is included code and not a
global function.  I can still do the __startup_secondary_64() function
and then look to incorporate verify_cpu into both __startup_64() and
__startup_secondary_64() as a post-patch to this series. At least the
secondary path will have a base C routine to which modifications can
be made in the future if needed.  How does that sound?

Thanks,
Tom

> Thanks,
>
>         tglx
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