On Wed, Aug 19, 2020 at 11:03:48AM -0500, Eric van Tassell wrote: > > > On 8/3/20 11:27 AM, Sean Christopherson wrote: > >On Sun, Aug 02, 2020 at 03:53:54PM -0500, Eric van Tassell wrote: > >> > >>On 7/31/20 3:25 PM, Sean Christopherson wrote: > >>>On Fri, Jul 24, 2020 at 06:54:46PM -0500, eric van tassell wrote: > >>>>Improve SEV guest startup time from O(n) to a constant by deferring > >>>>guest page pinning until the pages are used to satisfy nested page faults. > >>>> > >>>>Implement the code to do the pinning (sev_get_page) and the notifier > >>>>sev_set_spte_notify(). > >>>> > >>>>Track the pinned pages with xarray so they can be released during guest > >>>>termination. > >>> > >>>I like that SEV is trying to be a better citizen, but this is trading one > >>>hack for another. > >>> > >>> - KVM goes through a lot of effort to ensure page faults don't need to > >>> allocate memory, and this throws all that effort out the window. > >>> > >>can you elaborate on that? > > > >mmu_topup_memory_caches() is called from the page fault handlers before > >acquiring mmu_lock to pre-allocate shadow pages, PTE list descriptors, GFN > >arrays, etc... that may be needed to handle the page fault. This allows > >using standard GFP flags for the allocation and obviates the need for error > >handling in the consumers. > > > > I see what you meant. The issue that causes us to use this approach is that > we need to be able to unpin the pages when the VM exits. Yes, but using a software available flag in the SPTE to track pinned pages should be very doable.
