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Date: Tue, 21 Apr 2026 23:25:50 +0000
From: Yosry Ahmed <yosry@kernel.org>
To: Sean Christopherson <seanjc@google.com>
Cc: Peter Fang <peter.fang@intel.com>, Paolo Bonzini <pbonzini@redhat.com>, 
	Madhavan Srinivasan <maddy@linux.ibm.com>, Nicholas Piggin <npiggin@gmail.com>, 
	Ritesh Harjani <ritesh.list@gmail.com>, Michael Ellerman <mpe@ellerman.id.au>, 
	"Christophe Leroy (CS GROUP)" <chleroy@kernel.org>, Thomas Gleixner <tglx@kernel.org>, 
	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>, 
	kvm@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 3/3] KVM: Take gpa_t in kvm_vcpu_map[_readonly]()
Message-ID: <aegHZrDn3GouTpZf@google.com>
References: <20260408001137.3290444-1-peter.fang@intel.com>
 <20260408001137.3290444-4-peter.fang@intel.com>
 <aegDJssx-ZvbfggI@google.com>
 <aegF59gToidudIUC@google.com>
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In-Reply-To: <aegF59gToidudIUC@google.com>

On Tue, Apr 21, 2026 at 04:19:03PM -0700, Sean Christopherson wrote:
> On Tue, Apr 21, 2026, Yosry Ahmed wrote:
> > On Tue, Apr 07, 2026 at 05:11:30PM -0700, Peter Fang wrote:
> > > Move the conversion from a gpa_t to a gfn_t into kvm_vcpu_map() and
> > > kvm_vcpu_map_readonly() so that they take a gpa_t directly, reducing
> > > boilerplate at call sites.
> > > 
> > > __kvm_vcpu_map() still takes a gfn_t because guest page mapping is
> > > fundamentally GFN-based.
> > > 
> > > No functional change intended.
> > > 
> > > Compile-tested on x86 and ppc, which are the current users of these
> > > interfaces.
> > > 
> > > Suggested-by: Yosry Ahmed <yosry@kernel.org>
> > > Signed-off-by: Peter Fang <peter.fang@intel.com>
> > > ---
> > 
> > I was going to suggest a WARN in kvm_vcpu_map() and
> > kvm_vcpu_map_readonly() if the passed GPA is not page-aligned, but Sean
> > usually hates my paranoid WARN suggestions.
> 
> Heh, for good reason.  Adding such a WARN would be triggered by this code:
> 
>                 if (!kvm_vcpu_map(vcpu, vmcs12->posted_intr_desc_addr, map)) {
>                         vmx->nested.pi_desc =
>                                 (struct pi_desc *)(((void *)map->hva) +
>                                 offset_in_page(vmcs12->posted_intr_desc_addr));
> 
> The PI descriptor only needs to be 64-bit aligned, not page-aligned.

I didn't know that, thanks for pointing out. You meant 64-byte aligned
though, right?