On Wed, Jul 14, 2010 at 09:18:58PM +0800, Xiao Guangrong wrote: > > > Marcelo Tosatti wrote: > > On Wed, Jul 14, 2010 at 09:24:22AM +0800, Xiao Guangrong wrote: > >> > >> Marcelo Tosatti wrote: > >>> On Tue, Jul 13, 2010 at 05:45:27PM +0800, Xiao Guangrong wrote: > >>>> In speculative path, the page is not real write-access, no need mark it > >>>> dirty, so clear dirty bit in this path and later examine this bit when > >>>> we release the page > >>>> > >>>> Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxx> > >>>> --- > >>>> arch/x86/kvm/mmu.c | 24 +++++++++++------------- > >>>> 1 files changed, 11 insertions(+), 13 deletions(-) > >>> Unfortunately all pages that kvm creates translations for are marked > >>> dirty due to get_user_pages(w=1), except KSM which makes them read-only > >>> later. > >> Marcelo, i have looked into get_user_pages() function, but not catch where > >> to make page dirty, could you point it out for me? :-) > > > > See set_page_dirty call in mm/memory.c::follow_page. > > Yeah, you are right, and i want to use another way to do it since track dirty bit > is too heavy, also it's dangerous if we miss to set page dirty. > > How about just track access bit for speculative path, we set page both accessed and > dirty(if it's writable) only if the access bit is set? A useful thing to do would be to allow read-only mappings, in the fault path (Lai sent a few patches in that direction sometime ago but there was no follow up). So in the case of a read-only fault from the guest, you'd inform get_user_pages() that read-only access is acceptable (so swapcache pages can be mapped, or qemu can mprotect(PROT_READ) guest memory). -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
