On 7/12/22 3:18 PM, Chuck Zmudzinski wrote: > On 7/12/22 2:27 PM, Juergen Gross wrote: > > On 12.07.22 20:20, Chuck Zmudzinski wrote: > > > The commit 99c13b8c8896d7bcb92753bf > > > ("x86/mm/pat: Don't report PAT on CPUs that don't support it") > > > incorrectly failed to account for the case in init_cache_modes() when > > > CPUs do support PAT and falsely reported PAT to be disabled when in > > > fact PAT is enabled. In some environments, notably in Xen PV domains, > > > MTRR is disabled but PAT is still enabled, and that is the case > > > that the aforementioned commit failed to account for. > > > > > > As an unfortunate consequnce, the pat_enabled() function currently does > > > not correctly report that PAT is enabled in such environments. The fix > > > is implemented in init_cache_modes() by setting pat_bp_enabled to true > > > in init_cache_modes() for the case that commit 99c13b8c8896d7bcb92753bf > > > ("x86/mm/pat: Don't report PAT on CPUs that don't support it") failed > > > to account for. > > > > > > This patch fixes a regression that some users are experiencing with > > > Linux as a Xen Dom0 driving particular Intel graphics devices by > > > correctly reporting to the Intel i915 driver that PAT is enabled where > > > previously it was falsely reporting that PAT is disabled. > > > > > > Fixes: 99c13b8c8896d7bcb92753bf ("x86/mm/pat: Don't report PAT on CPUs that don't support it") > > > Cc: stable@xxxxxxxxxxxxxxx > > > Signed-off-by: Chuck Zmudzinski <brchuckz@xxxxxxx> > > > --- > > > Reminder: This patch is a regression fix that is needed on stable > > > versions 5.17 and later. > > > > > > arch/x86/mm/pat/memtype.c | 12 ++++++++++++ > > > 1 file changed, 12 insertions(+) > > > > > > diff --git a/arch/x86/mm/pat/memtype.c b/arch/x86/mm/pat/memtype.c > > > index d5ef64ddd35e..0f2417bd1b40 100644 > > > --- a/arch/x86/mm/pat/memtype.c > > > +++ b/arch/x86/mm/pat/memtype.c > > > @@ -315,6 +315,18 @@ void init_cache_modes(void) > > > PAT(4, WB) | PAT(5, WT) | PAT(6, UC_MINUS) | PAT(7, UC); > > > } > > > > > > + else if (!pat_bp_enabled) { > > > > Please put the "else if {" into the same line as the "}" above. > > > > > + /* > > > + * In some environments, specifically Xen PV, PAT > > > + * initialization is skipped because MTRRs are disabled even > > > + * though PAT is available. In such environments, set PAT to > > > + * enabled to correctly indicate to callers of pat_enabled() > > > + * that CPU support for PAT is available. > > > + */ > > > + pat_bp_enabled = true; > > > + pr_info("x86/PAT: PAT enabled by init_cache_modes\n"); > > > > Wrong indentation. > > > > > + } > > > + > > > __init_cache_modes(pat); > > > } > > > > > > > Any reason you didn't fix the "nopat" issue Jan mentioned? > > > > I asked you twice to add this fix. > > > > > > Juergen > > Sorry, I did not see your request. I will resend with the fix > for "nopat" and the other style issues you mentioned. > > Chuck I will also re-compile and test the new patch before sending v2 and unless Jan objects, I should acknowledge Jan as co-author of the patch since I will be using parts of his proposed patch to fix the "nopat" issue, so I also need to get his sign-off before sending v2. Jan, how should I obtain your sign-off? Chuck Chuck