Re: [PATCH 6/9] KVM: MMU: introduce the framework to check reserved bits on sptes

From: Xiao Guangrong <guangrong.xiao@linux.intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: gleb@kernel.org, mtosatti@redhat.com, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 6/9] KVM: MMU: introduce the framework to check reserved bits on sptes
Date: Tue, 4 Aug 2015 21:10:09 +0800	[thread overview]
Message-ID: <55C0B9B1.9070504@linux.intel.com> (raw)
In-Reply-To: <55C0AC9C.6070606@redhat.com>

On 08/04/2015 08:14 PM, Paolo Bonzini wrote:
>
>
> On 04/08/2015 12:59, Xiao Guangrong wrote:
>> +/*
>> + * the page table on host is the shadow page table for the page
>> + * table in guest or amd nested guest, its mmu features completely
>> + * follow the features in guest.
>> + */
>> +void
>> +reset_shadow_rsvds_bits_mask(struct kvm_vcpu *vcpu, struct kvm_mmu *context)
>> +{
>> +	__reset_rsvds_bits_mask(vcpu, &context->shadow_rsvd_check,
>> +				boot_cpu_data.x86_phys_bits,
>> +				context->shadow_root_level, context->nx,
>
> This should be cpu_has_nx, I think.

cpu_has_nx() checks the feature on host CPU, however, this is the shadow
page table which completely follow guest's features.

E.g, if guest does not execution-protect the physical page, then
KVM does not do it either.

>
>> +				guest_cpuid_has_gbpages(vcpu),
>
> This should be cpu_has_gbpages.

E.g, if guest does not use 1G page size, it's also not used in shadow page
table.

>
>> is_pse(vcpu));
>
> This should be cpu_has_pse.

E.g, guest does no use 4M page size, then KVM does not use it either.

BTW, cpu_pse only hurts 32 bit page table which is not used by shadow
page table (32 PAE and 64 Long mode are used in shadow page).

Only tdp only follows host CPU's features, KVM does not use NX to
protect the page, so i always mark it as false in
reset_tdp_shadow_rsvds_bits_mask().