Re: [PATCH] KVM: MMU: record maximum physical address width in kvm_mmu_extended_role

[Yu Zhang]

On Wed, Feb 20, 2019 at 03:06:10PM +0100, Vitaly Kuznetsov wrote:
> Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx> writes:
> 
> > Previously, commit 7dcd57552008 ("x86/kvm/mmu: check if tdp/shadow
> > MMU reconfiguration is needed") offered some optimization to avoid
> > the unnecessary reconfiguration. Yet one scenario is broken - when
> > cpuid changes VM's maximum physical address width, reconfiguration
> > is needed to reset the reserved bits.  Also, the TDP may need to
> > reset its shadow_root_level when this value is changed.
> >
> > To fix this, a new field, maxphyaddr, is introduced in the extended
> > role structure to keep track of the configured guest physical address
> > width.
> >
> > Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
> > ---
> > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > Cc: "Radim KrÄmÃÅ" <rkrcmar@xxxxxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Borislav Petkov <bp@xxxxxxxxx>
> > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > ---
> >  arch/x86/include/asm/kvm_host.h | 1 +
> >  arch/x86/kvm/mmu.c              | 1 +
> >  2 files changed, 2 insertions(+)
> >
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index 4660ce9..be87f71 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -299,6 +299,7 @@ struct kvm_mmu_memory_cache {
> >  		unsigned int cr4_smap:1;
> >  		unsigned int cr4_smep:1;
> >  		unsigned int cr4_la57:1;
> > +		unsigned int maxphyaddr:6;
> >  	};
> >  };
> >  
> > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> > index ce770b4..2b74505 100644
> > --- a/arch/x86/kvm/mmu.c
> > +++ b/arch/x86/kvm/mmu.c
> > @@ -4769,6 +4769,7 @@ static union kvm_mmu_extended_role kvm_calc_mmu_role_ext(struct kvm_vcpu *vcpu)
> >  	ext.cr4_pse = !!is_pse(vcpu);
> >  	ext.cr4_pke = !!kvm_read_cr4_bits(vcpu, X86_CR4_PKE);
> >  	ext.cr4_la57 = !!kvm_read_cr4_bits(vcpu, X86_CR4_LA57);
> > +	ext.maxphyaddr = cpuid_maxphyaddr(vcpu);
> >  
> >  	ext.valid = 1;
> 
> It seems that we can now drop 'valid' from role_ext as maxphyaddr can't
> be 0.

Thanks, Vitaly. Yes, we can drop this field. :)

> 
> Reviewed-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> 
> -- 
> Vitaly
> 

B.R.
Yu