linux-kernel - Re: [PATCH RESEND v4 0/9] Enable Sub-page Write Protection Support

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Date:   Wed, 14 Aug 2019 16:06:07 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        sean.j.christopherson@...el.com, mst@...hat.com,
        rkrcmar@...hat.com, jmattson@...gle.com, yu.c.zhang@...el.com,
        alazar@...defender.com
Subject: Re: [PATCH RESEND v4 0/9] Enable Sub-page Write Protection Support

On 14/08/19 16:02, Yang Weijiang wrote:
> On Wed, Aug 14, 2019 at 02:36:30PM +0200, Paolo Bonzini wrote:
>> On 14/08/19 09:03, Yang Weijiang wrote:
>>> EPT-Based Sub-Page write Protection(SPP)is a HW capability which allows
>>> Virtual Machine Monitor(VMM) to specify write-permission for guest
>>> physical memory at a sub-page(128 byte) granularity. When this
>>> capability is enabled, the CPU enforces write-access check for sub-pages
>>> within a 4KB page.
>>>
>>> The feature is targeted to provide fine-grained memory protection for
>>> usages such as device virtualization, memory check-point and VM
>>> introspection etc.
>>>
>>> SPP is active when the "sub-page write protection" (bit 23) is 1 in
>>> Secondary VM-Execution Controls. The feature is backed with a Sub-Page
>>> Permission Table(SPPT), SPPT is referenced via a 64-bit control field
>>> called Sub-Page Permission Table Pointer (SPPTP) which contains a
>>> 4K-aligned physical address.
>>>
>>> Right now, only 4KB physical pages are supported for SPP. To enable SPP
>>> for certain physical page, we need to first make the physical page
>>> write-protected, then set bit 61 of the corresponding EPT leaf entry. 
>>> While HW walks EPT, if bit 61 is set, it traverses SPPT with the guset
>>> physical address to find out the sub-page permissions at the leaf entry.
>>> If the corresponding bit is set, write to sub-page is permitted,
>>> otherwise, SPP induced EPT violation is generated.
>>
>> Still no testcases?
>>
>> Paolo
> 
> Hi, Paolo,
> The testcases are included in selftest: https://lkml.org/lkml/2019/6/18/1197
> 

Good, thanks!

Paolo