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SubjectRe: [PATCH 2/2] KVM: MMU: document smap_andnot_wp


On 11/05/2015 16:55, Xiao Guangrong wrote:
> Document this new role field
>
> Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
> ---
> Documentation/virtual/kvm/mmu.txt | 18 ++++++++++++++----
> 1 file changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/virtual/kvm/mmu.txt b/Documentation/virtual/kvm/mmu.txt
> index 53838d9..c59bd9b 100644
> --- a/Documentation/virtual/kvm/mmu.txt
> +++ b/Documentation/virtual/kvm/mmu.txt
> @@ -169,6 +169,10 @@ Shadow pages contain the following information:
> Contains the value of cr4.smep && !cr0.wp for which the page is valid
> (pages for which this is true are different from other pages; see the
> treatment of cr0.wp=0 below).
> + role.smap_andnot_wp:
> + Contains the value of cr4.smap && !cr0.wp for which the page is valid
> + (pages for which this is true are different from other pages; see the
> + treatment of cr0.wp=0 below).
> gfn:
> Either the guest page table containing the translations shadowed by this
> page, or the base page frame for linear translations. See role.direct.
> @@ -344,10 +348,16 @@ on fault type:
>
> (user write faults generate a #PF)
>
> -In the first case there is an additional complication if CR4.SMEP is
> -enabled: since we've turned the page into a kernel page, the kernel may now
> -execute it. We handle this by also setting spte.nx. If we get a user
> -fetch or read fault, we'll change spte.u=1 and spte.nx=gpte.nx back.
> +In the first case there are two additional complications:
> +- if CR4.SMEP is enabled: since we've turned the page into a kernel page,
> + the kernel may now execute it. We handle this by also setting spte.nx.
> + If we get a user fetch or read fault, we'll change spte.u=1 and
> + spte.nx=gpte.nx back.
> +- if CR4.SMAP is disabled: since the page has been changed to a kernel
> + page, it can not be reused when CR4.SMAP is enabled. We set
> + CR4.SMAP && !CR0.WP into shadow page's role to avoid this case. Note,
> + here we do not care the case that CR4.SMAP is enabled since KVM will
> + directly inject #PF to guest due to failed permission check.
>
> To prevent an spte that was converted into a kernel page with cr0.wp=0
> from being written by the kernel after cr0.wp has changed to 1, we make
>

Thanks, squashed with 1/2 and both applied.

Paolo


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