linux-kernel - Re: [PATCH v5 0/9] Enable Sub-page Write Protection Support

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Date:   Fri, 11 Oct 2019 15:50:33 +0800
From:   Yang Weijiang <weijiang.yang@...el.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     Yang Weijiang <weijiang.yang@...el.com>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        yu.c.zhang@...el.com, alazar@...defender.com
Subject: Re: [PATCH v5 0/9] Enable Sub-page Write Protection Support

On Thu, Oct 10, 2019 at 02:42:51PM -0700, Jim Mattson wrote:
> On Tue, Sep 17, 2019 at 1:52 AM Yang Weijiang <weijiang.yang@...el.com> 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.
> >
> > To enable SPP for certain physical page, the gfn should be first mapped
> > to a 4KB entry, 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.
> 
> How do you handle sub-page permissions for instructions emulated by kvm?
How about checking if the gpa is SPP protected, if it is, inject some
exception to guest?