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

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Date:   Wed, 20 Feb 2019 15:06:10 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Yu Zhang <yu.c.zhang@...ux.intel.com>, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        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

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.

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

-- 
Vitaly