linux-kernel - Re: [PATCH 14/16] KVM: x86/mmu: Set kvm_page_fault.hva to KVM_HVA_ERR

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Message-ID: <ZekR4j-hsXDFD6K2@google.com>
Date: Wed, 6 Mar 2024 17:01:22 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Kai Huang <kai.huang@...el.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Yan Zhao <yan.y.zhao@...el.com>, Isaku Yamahata <isaku.yamahata@...el.com>, 
	Michael Roth <michael.roth@....com>, Yu Zhang <yu.c.zhang@...ux.intel.com>, 
	Chao Peng <chao.p.peng@...ux.intel.com>, Fuad Tabba <tabba@...gle.com>, 
	David Matlack <dmatlack@...gle.com>
Subject: Re: [PATCH 14/16] KVM: x86/mmu: Set kvm_page_fault.hva to
 KVM_HVA_ERR_BAD for "no slot" faults

On Thu, Mar 07, 2024, Kai Huang wrote:
> 
> 
> On 28/02/2024 3:41 pm, Sean Christopherson wrote:
> > Explicitly set fault->hva to KVM_HVA_ERR_BAD when handling a "no slot"
> > fault to ensure that KVM doesn't use a bogus virtual address, e.g. if
> > there *was* a slot but it's unusable (APIC access page), or if there
> > really was no slot, in which case fault->hva will be '0' (which is a
> > legal address for x86).
> > 
> > Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> > ---
> >   arch/x86/kvm/mmu/mmu.c | 1 +
> >   1 file changed, 1 insertion(+)
> > 
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 4dee0999a66e..43f24a74571a 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -3325,6 +3325,7 @@ static int kvm_handle_noslot_fault(struct kvm_vcpu *vcpu,
> >   	fault->slot = NULL;
> >   	fault->pfn = KVM_PFN_NOSLOT;
> >   	fault->map_writable = false;
> > +	fault->hva = KVM_HVA_ERR_BAD;
> >   	/*
> >   	 * If MMIO caching is disabled, emulate immediately without
> 
> Not sure why this cannot be merged to the previous one?

Purely because (before the previous patch) kvm_faultin_pfn() only paved over pfn,
slot, and map_writable.  I highly doubt clobbering hva will break anything, but
just in case...