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(-) -- 2.35.3
