KVM: SVM: Drop pointless masking of kernel page pa's with AVIC HPA masks

				      ^^^^^^^^^^^^^^^^
Just "physical addresses", or perhaps "HPAs"?

On Wed, Jun 11, 2025 at 03:45:12PM -0700, Sean Christopherson wrote:

Drop AVIC_HPA_MASK and all its users, the mask is just the 4KiB-aligned
maximum theoretical physical address for x86-64 CPUs, as x86-64 is
currently defined (going beyond PA52 would require an entirely new paging
mode, which would arguably create a new, different architecture).

All usage in KVM masks the result of page_to_phys(), which on x86-64 is
guaranteed to be 4KiB aligned and a legal physical address; if either of
those requirements doesn't hold true, KVM has far bigger problems.

Drop masking the avic_backing_page with
AVIC_PHYSICAL_ID_ENTRY_BACKING_PAGE_MASK for all the same reasons, but
keep the macro even though it's unused in functional code.  It's a
distinct architectural define, and having the definition in software
helps visualize the layout of an entry.  And to be hyper-paranoid about
MAXPA going beyond 52, add a compile-time assert to ensure the kernel's
maximum supported physical address stays in bounds.

The unnecessary masking in avic_init_vmcb() also incorrectly assumes that
SME's C-bit resides between bits 51:11; that holds true for current CPUs,
but isn't required by AMD's architecture:

  In some implementations, the bit used may be a physical address bit

Key word being "may".

Opportunistically use the GENMASK_ULL() version for
AVIC_PHYSICAL_ID_ENTRY_BACKING_PAGE_MASK, which is far more readable
than a set of repeating Fs.

Makes sense.
Reviewed-by: Naveen N Rao (AMD) <naveen@kernel.org>

- Naveen