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

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Message-ID: <e970156b-b4e8-1745-c774-455756f237f0@redhat.com>
Date:   Fri, 22 Feb 2019 19:24:07 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Yu Zhang <yu.c.zhang@...ux.intel.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 20/02/19 08:06, Yu Zhang wrote:
> Hi Paolo, any comments on this patch? And the other one(kvm: x86: Return
> LA57 feature based on hardware capability )? :-)

Queued both, thanks.

Paolo

> On Fri, Feb 01, 2019 at 12:09:23AM +0800, Yu Zhang wrote:
>> 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;
>>  
>> -- 
>> 1.9.1
>>
> 
> Thanks
> Yu
>