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Message-ID: <7c31e31d0f0ad3f40619f8e0ecf67f1e3d3eef5f.camel@infradead.org>
Subject: Re: [PATCH v12 08/20] KVM: pfncache: allow a cache to be activated
 with a fixed (userspace) HVA
From: David Woodhouse <dwmw2@infradead.org>
To: Sean Christopherson <seanjc@google.com>, Paul Durrant <paul@xen.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>, Jonathan Corbet <corbet@lwn.net>, 
 Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
 Borislav Petkov <bp@alien8.de>, Dave Hansen <dave.hansen@linux.intel.com>,
 x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,  Shuah Khan
 <shuah@kernel.org>, kvm@vger.kernel.org, linux-doc@vger.kernel.org, 
 linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Christian
 Borntraeger <borntraeger@linux.ibm.com>, Janosch Frank
 <frankja@linux.ibm.com>, Claudio Imbrenda <imbrenda@linux.ibm.com>, David
 Hildenbrand <david@redhat.com>
Date: Tue, 06 Feb 2024 20:13:09 -0800
In-Reply-To: <ZcMBDP6H5PRo5C2d@google.com>
References: <20240115125707.1183-1-paul@xen.org>
	 <20240115125707.1183-9-paul@xen.org> <ZcMBDP6H5PRo5C2d@google.com>
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On Tue, 2024-02-06 at 20:03 -0800, Sean Christopherson wrote:
> +s390 folks (question on kvm_is_error_gpa() for ya)
>=20
> On Mon, Jan 15, 2024, Paul Durrant wrote:
> > @@ -1398,7 +1414,9 @@ void kvm_gpc_deactivate(struct gfn_to_pfn_cache *=
gpc);
> > =C2=A0 static inline void kvm_gpc_mark_dirty(struct gfn_to_pfn_cache *g=
pc)
> > =C2=A0 {
> > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0lockdep_assert_held(&gp=
c->lock);
> > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0mark_page_dirty_in_slot(gpc-=
>kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
> > +
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if (gpc->gpa !=3D KVM_XEN_IN=
VALID_GPA)
>=20
> KVM_XEN_INVALID_GPA absolutely doesn't belong in common code.=C2=A0 Not t=
o mention
> that it will break when Paolo (rightly) moves it to an x86 header.
>=20
> https://lore.kernel.org/all/20240131233056.10845-3-pbonzini@redhat.com

We can use plain INVALID_GPA for that, I think. ISTR the reason we have
a separate KVM_XEN_INVALID_GPA is because that's a userspace API.

..

> But!  kvm_is_error_gpa() already exists, and it very, very sneakily
> does a memslot lookup and checks for a valid HVA.

Hm, that doesn't sound as fast as simple comparison. We also can't do
it from kvm_gpc_check(), can we?


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