On Tue, 2019-08-13 at 00:49 -0700, Isaku Yamahata wrote: > On Fri, Aug 09, 2019 at 07:51:17PM +0000, > "Kani, Toshi" <toshi.k...@hpe.com> wrote: > > > On Fri, 2019-08-09 at 09:06 +0200, Borislav Petkov wrote: > > > On Thu, Aug 08, 2019 at 08:54:17PM -0700, Isaku Yamahata wrote: > > > > Make PAT(Page Attribute Table) independent from > > > > MTRR(Memory Type Range Register). > > > > Some environments (mainly virtual ones) support only PAT, but not MTRR > > > > because PAT replaces MTRR. > > > > It's tricky and no gain to support both MTRR and PAT except > > > > compatibility. > > > > So some VM technologies don't support MTRR, but only PAT. > > > > I do not think it is technically correct on bare metal. AFAIK, MTRR is > > still the only way to setup cache attribute in real-mode, which BIOS SMI > > handler relies on in SMM. > > Then you're claiming if it's baremetal, both MTRR and PAT should be > enabled/disabled at the same time?
No, I did not say that. My point: - Your statement of MTTR being useless is not correct. It's still used. The OS should leave the MTTR hand-off state. I agree with you in general that PAT and MTTR init should be independent. However, as Boris said, please verify the impact of your change. As I mentioned in the Xen's example, hypervisor may have non- default PAT hand-off setting. Thanks, -Toshi
