On 20/11/2020 12:48, Jan Beulich wrote: > On 04.11.2020 08:56, 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> >> --- >> v2: Don't change type's type. > Ping?
Ping what? There is still nothing addressing my concerns from v1. To re-iterate - this is a very subtle change, in a very complicated piece of migration. As the problems described do not manifest in practice, it is vital to understand why. ~Andrew
