Re: [PATCH v3] selftests: KVM: avoid failures due to reserved HyperTransport region

[Sean Christopherson <seanjc@google.com>]

On Thu, Dec 09, 2021, Paolo Bonzini wrote:
> AMD proceessors define an address range that is reserved by HyperTransport
> and causes a failure if used for guest physical addresses.  Avoid
> selftests failures by reserving those guest physical addresses; the
> rules are:
> 
> - On parts with <40 bits, its fully hidden from software.
> 
> - Before Fam17h, it was always 12G just below 1T, even if there was more
> RAM above this location.  In this case we just not use any RAM above 1T.
> 
> - On Fam17h and later, it is variable based on SME, and is either just
> below 2^48 (no encryption) or 2^43 (encryption).
> 
> Fixes: ef4c9f4f6546 ("KVM: selftests: Fix 32-bit truncation of vm_get_max_gfn()")
> Cc: stable@vger.kernel.org
> Cc: David Matlack <dmatlack@google.com>
> Reported-by: Maxim Levitsky <mlevitsk@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> Message-Id: <20210805105423.412878-1-pbonzini@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Reviewed-and-tested-by: Sean Christopherson <seanjc@google.com>

> +	/*
> +	 * Otherwise it's at the top of the physical address
> +	 * space, possibly reduced due to SME by bits 11:6 of
> +	 * CPUID[0x8000001f].EBX.  Use the old conservative
> +	 * value if MAXPHYADDR is not enumerated.

It'd be nice to run these out to 80 chars when you apply.