Messages in this thread | | | Date | Tue, 12 Jul 2022 20:27:33 +0200 | Subject | Re: [PATCH] x86/PAT: Report PAT on CPUs that support PAT without MTRR | From | Juergen Gross <> |
| |
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@vger.kernel.org > Signed-off-by: Chuck Zmudzinski <brchuckz@aol.com> > --- > 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 [unhandled content-type:application/pgp-keys][unhandled content-type:application/pgp-signature] | |