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x86: Decouple PAT and MTRR handling

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Today, PAT is usable only with MTRR being active, with some nasty tweaks
to make PAT usable when running as a Xen PV guest which doesn't support
MTRR.

The reason for this coupling is that both PAT MSR changes and MTRR
changes require a similar sequence and so full PAT support was added
using the already available MTRR handling.

Xen PV PAT handling can work without MTRR, as it just needs to consume
the PAT MSR setting done by the hypervisor without the ability and need
to change it. This in turn has resulted in a convoluted initialization
sequence and wrong decisions regarding cache mode availability due to
misguiding PAT availability flags.

Fix all of that by allowing to use PAT without MTRR and by reworking
the current PAT initialization sequence to match better with the newly
introduced generic cache initialization.

This removes the need of the recently added pat_force_disabled flag, so
remove the remnants of the patch adding it.

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20221102074713.21493-14-jgross@suse.com
Signed-off-by: Borislav Petkov <bp@suse.de>
This commit is contained in:
Juergen Gross
2022-11-02 08:47:10 +01:00
committed by Borislav Petkov
parent 0b9a6a8bed
commit adfe7512e1
5 changed files with 57 additions and 128 deletions
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arch/x86/kernel/setup.c
+1 -12
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@@ -1075,23 +1075,12 @@ void __init setup_arch(char **cmdline_p)
max_pfn = e820__end_of_ram_pfn();
/* update e820 for memory not covered by WB MTRRs */
if (IS_ENABLED(CONFIG_MTRR))
cache_bp_init();
else
pat_disable("PAT support disabled because CONFIG_MTRR is disabled in the kernel.");
cache_bp_init();
if (mtrr_trim_uncached_memory(max_pfn))
max_pfn = e820__end_of_ram_pfn();
max_possible_pfn = max_pfn;
/*
* This call is required when the CPU does not support PAT. If
* mtrr_bp_init() invoked it already via pat_init() the call has no
* effect.
*/
init_cache_modes();
/*
* Define random base addresses for memory sections after max_pfn is
* defined and before each memory section base is used.