On 7/16/2022 7:32 AM, Chuck Zmudzinski wrote: > On 7/15/2022 10:25 AM, Juergen Gross wrote: > > Today PAT can't be used without MTRR being available, unless MTRR is at > > least configured via CONFIG_MTRR and the system is running as Xen PV > > guest. In this case PAT is automatically available via the hypervisor, > > but the PAT MSR can't be modified by the kernel and MTRR is disabled. > > > > As an additional complexity the availability of PAT can't be queried > > via pat_enabled() in the Xen PV case, as the lack of MTRR will set PAT > > to be disabled. This leads to some drivers believing that not all cache > > modes are available, resulting in failures or degraded functionality. > > > > The same applies to a kernel built with no MTRR support: it won't > > allow to use the PAT MSR, even if there is no technical reason for > > that, other than setting up PAT on all cpus the same way (which is a > > requirement of the processor's cache management) is relying on some > > MTRR specific code. > > > > Fix all of that by: > > > > - moving the function needed by PAT from MTRR specific code one level > > up > > - adding a PAT indirection layer supporting the 3 cases "no or disabled > > PAT", "PAT under kernel control", and "PAT under Xen control" > > - removing the dependency of PAT on MTRR > > > > Juergen Gross (3): > > x86: move some code out of arch/x86/kernel/cpu/mtrr > > x86: add wrapper functions for mtrr functions handling also pat > > x86: decouple pat and mtrr handling > > > > arch/x86/include/asm/memtype.h | 13 ++- > > arch/x86/include/asm/mtrr.h | 27 ++++-- > > arch/x86/include/asm/processor.h | 10 +++ > > arch/x86/kernel/cpu/common.c | 123 +++++++++++++++++++++++++++- > > arch/x86/kernel/cpu/mtrr/generic.c | 90 ++------------------ > > arch/x86/kernel/cpu/mtrr/mtrr.c | 58 ++++--------- > > arch/x86/kernel/cpu/mtrr/mtrr.h | 1 - > > arch/x86/kernel/setup.c | 12 +-- > > arch/x86/kernel/smpboot.c | 8 +- > > arch/x86/mm/pat/memtype.c | 127 +++++++++++++++++++++-------- > > arch/x86/power/cpu.c | 2 +- > > arch/x86/xen/enlighten_pv.c | 4 + > > 12 files changed, 289 insertions(+), 186 deletions(-) > > > > This patch series seems related to the regression reported > here on May 5, 2022: I'm sorry, the date of that report was May 4, 2022, not May 5, 2022 - just to avoid any doubt about which regression I am referring to. Chuck > > https://lore.kernel.org/regressions/YnHK1Z3o99eMXsVK@mail-itl/ > > I am experiencing that regression or a very similar regression that is caused by the same commit: bdd8b6c98239cad ("drm/i915: replace X86_FEATURE_PAT with pat_enabled()") > and could test this patch > on my system. > > Can you confirm that with this patch series you are trying > to fix that regression? > > Chuck Chuck
