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Re: [PATCH 1/2] x86/shadow: slightly consolidate sh_unshadow_for_p2m_change()


  • To: Jan Beulich <jbeulich@xxxxxxxx>
  • From: George Dunlap <George.Dunlap@xxxxxxxxxx>
  • Date: Fri, 24 Jun 2022 19:16:33 +0000
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  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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  • Thread-topic: [PATCH 1/2] x86/shadow: slightly consolidate sh_unshadow_for_p2m_change()


> On 9 Dec 2021, at 11:26, Jan Beulich <jbeulich@xxxxxxxx> wrote:
> 
> In preparation for reactivating the presently dead 2M page path of the
> function,
> - also deal with the case of replacing an L1 page table all in one go,
> - pull common checks out of the switch(). This includes extending a
>  _PAGE_PRESENT check to L1 as well, which presumably was deemed
>  redundant with p2m_is_valid() || p2m_is_grant(), but I think we are
>  better off being explicit in all cases,
> - replace a p2m_is_ram() check in the 2M case by an explicit
>  _PAGE_PRESENT one, to make more obvious that the subsequent
>  l1e_get_mfn() actually retrieves something that is actually an MFN.

Each of these changes requires careful checking to make sure there aren’t any 
bugs introduced.  I’d feel much more comfortable giving an R-b of they were 
broken out into separate patches.

 -George

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