From: Sean Christopherson <seanjc@google.com>
To: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
linux-kernel@vger.kernel.org, Joerg Roedel <joro@8bytes.org>,
Tom Lendacky <thomas.lendacky@amd.com>,
Brijesh Singh <brijesh.singh@amd.com>,
Peter Gonda <pgonda@google.com>
Subject: Re: [PATCH] x86/cpu/AMD: Adjust x86_phys_bits to account for reduced PA in SEV-* guests
Date: Wed, 17 Mar 2021 14:19:27 -0700 [thread overview]
Message-ID: <YFJyX/MludiiS+dN@google.com> (raw)
In-Reply-To: <YFJbzIrGLXu2UsFv@google.com>
On Wed, Mar 17, 2021, Sean Christopherson wrote:
> On Wed, Mar 17, 2021, Borislav Petkov wrote:
> > IOW, you have c_bit so your valid address space is [0 .. c_bit-1] no?
>
> I haven't found anything in the GHCB that dictates that MAXPHYADDR == C_BIT-1,
> or more specifically that MAXPHYADDR == C_BIT - PhysAddrReduction. E.g. AFAICT,
> a VMM could do C_BIT=47, MAXPHYADDR=36, PhysAddrReduction=0, and that would be
> allowed by the GHCB.
>
> Forcing "c->x86_phys_bits = c_bit - 1" doesn't seem like it would break anything,
> but it's also technically wrong.
On the other hand, "C_BIT=47, MAXPHYADDR=36, PhysAddrReduction=0" would mean the
C-bit is an illegal PA bit from the guest's perspective. That's rather
nonsensical, but also not technically disallowed by the APM or GHCB specs.
next prev parent reply other threads:[~2021-03-17 21:20 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-17 18:32 [PATCH] x86/cpu/AMD: Adjust x86_phys_bits to account for reduced PA in SEV-* guests Sean Christopherson
2021-03-17 19:11 ` Borislav Petkov
2021-03-17 19:43 ` Sean Christopherson
2021-03-17 21:19 ` Sean Christopherson [this message]
2021-03-17 21:51 ` Peter Gonda
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