linux-kernel - Re: [PATCH] KVM: MMU: record maximum physical address width in kvm_mmu_extended

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Message-ID: <20190221065819.fu2lvakahoby5mcc@linux.intel.com>
Date:   Thu, 21 Feb 2019 14:58:19 +0800
From:   Yu Zhang <yu.c.zhang@...ux.intel.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: MMU: record maximum physical address width in
 kvm_mmu_extended_role

On Wed, Feb 20, 2019 at 03:06:10PM +0100, Vitaly Kuznetsov wrote:
> Yu Zhang <yu.c.zhang@...ux.intel.com> 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@...ux.intel.com>
> > ---
> > Cc: Paolo Bonzini <pbonzini@...hat.com>
> > Cc: "Radim Krčmář" <rkrcmar@...hat.com>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Cc: Borislav Petkov <bp@...en8.de>
> > Cc: "H. Peter Anvin" <hpa@...or.com>
> > Cc: linux-kernel@...r.kernel.org
> > ---
> >  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@...hat.com>
> 
> -- 
> Vitaly
> 

B.R.
Yu