On 23.11.2020 12:48, Roger Pau Monné wrote: > On Wed, Nov 04, 2020 at 08:56:50AM +0100, Jan Beulich wrote: >> When a page table page gets de-validated, its type reference count drops >> to zero (and PGT_validated gets cleared), but its type remains intact. >> XEN_DOMCTL_getpageframeinfo3, therefore, so far reported prior usage for >> such pages. An intermediate write to such a page via e.g. >> MMU_NORMAL_PT_UPDATE, however, would transition the page's type to >> PGT_writable_page, thus altering what XEN_DOMCTL_getpageframeinfo3 would >> return. In libxc the decision which pages to normalize / localize >> depends solely on the type returned from the domctl. As a result without >> further precautions the guest won't be able to tell whether such a page >> has had its (apparent) PTE entries transitioned to the new MFNs. >> >> Add a check of PGT_validated, thus consistently avoiding normalization / >> localization in the tool stack. >> >> Also use XEN_DOMCTL_PFINFO_NOTAB in the variable's initializer instead >> open coding it. >> >> Signed-off-by: Jan Beulich <jbeul...@suse.com> > > Acked-by: Roger Pau Monné <roger....@citrix.com>
Thanks. > Maybe the switch could be avoided if the page is not validated or > broken? Not that I care that much. It certainly could be, but it didn't seem worth the code churn to me. Jan
