On 9/27/19 4:15 AM, Paolo Bonzini wrote: > Shadow paging is fundamentally incompatible with the page-modification > log, because the GPAs in the log come from the wrong memory map. > In particular, for the EPT page-modification log, the GPAs in the log come > from L2 rather than L1. (If there was a non-EPT page-modification log, > we couldn't use it for shadow paging because it would log GVAs rather > than GPAs). > > Therefore, we need to rely on write protection to record dirty pages. > This has the side effect of bypassing PML, since writes now result in an > EPT violation vmexit. > > This is relatively easy to add to KVM, because pretty much the only place > that needs changing is spte_clear_dirty. The first access to the page > already goes through the page fault path and records the correct GPA; > it's only subsequent accesses that are wrong. Therefore, we can equip > set_spte (where the first access happens) to record that the SPTE will > have to be write protected, and then spte_clear_dirty will use this > information to do the right thing. > > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> > --- Reviewed-by: Junaid Shahid <junaids@xxxxxxxxxx>
