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authorJan Beulich <jbeulich@suse.com>2022-04-28 17:50:29 +0300
committerBorislav Petkov <bp@suse.de>2022-08-15 11:51:23 +0300
commit72cbc8f04fe2fa93443c0fcccb7ad91dfea3d9ce (patch)
tree9ae0c7a7b32b04ada05d833de1471a31e44874d2 /arch/x86/mm
parent568035b01cfb107af8d2e4bd2fb9aea22cf5b868 (diff)
downloadlinux-72cbc8f04fe2fa93443c0fcccb7ad91dfea3d9ce.tar.xz
x86/PAT: Have pat_enabled() properly reflect state when running on Xen
After commit ID in the Fixes: tag, pat_enabled() returns false (because of PAT initialization being suppressed in the absence of MTRRs being announced to be available). This has become a problem: the i915 driver now fails to initialize when running PV on Xen (i915_gem_object_pin_map() is where I located the induced failure), and its error handling is flaky enough to (at least sometimes) result in a hung system. Yet even beyond that problem the keying of the use of WC mappings to pat_enabled() (see arch_can_pci_mmap_wc()) means that in particular graphics frame buffer accesses would have been quite a bit less optimal than possible. Arrange for the function to return true in such environments, without undermining the rest of PAT MSR management logic considering PAT to be disabled: specifically, no writes to the PAT MSR should occur. For the new boolean to live in .init.data, init_cache_modes() also needs moving to .init.text (where it could/should have lived already before). [ bp: This is the "small fix" variant for stable. It'll get replaced with a proper PAT and MTRR detection split upstream but that is too involved for a stable backport. - additional touchups to commit msg. Use cpu_feature_enabled(). ] Fixes: bdd8b6c98239 ("drm/i915: replace X86_FEATURE_PAT with pat_enabled()") Signed-off-by: Jan Beulich <jbeulich@suse.com> Signed-off-by: Borislav Petkov <bp@suse.de> Acked-by: Ingo Molnar <mingo@kernel.org> Cc: <stable@vger.kernel.org> Cc: Juergen Gross <jgross@suse.com> Cc: Lucas De Marchi <lucas.demarchi@intel.com> Link: https://lore.kernel.org/r/9385fa60-fa5d-f559-a137-6608408f88b0@suse.com
Diffstat (limited to 'arch/x86/mm')
-rw-r--r--arch/x86/mm/pat/memtype.c10
1 files changed, 9 insertions, 1 deletions
diff --git a/arch/x86/mm/pat/memtype.c b/arch/x86/mm/pat/memtype.c
index d5ef64ddd35e..66a209f7eb86 100644
--- a/arch/x86/mm/pat/memtype.c
+++ b/arch/x86/mm/pat/memtype.c
@@ -62,6 +62,7 @@
static bool __read_mostly pat_bp_initialized;
static bool __read_mostly pat_disabled = !IS_ENABLED(CONFIG_X86_PAT);
+static bool __initdata pat_force_disabled = !IS_ENABLED(CONFIG_X86_PAT);
static bool __read_mostly pat_bp_enabled;
static bool __read_mostly pat_cm_initialized;
@@ -86,6 +87,7 @@ void pat_disable(const char *msg_reason)
static int __init nopat(char *str)
{
pat_disable("PAT support disabled via boot option.");
+ pat_force_disabled = true;
return 0;
}
early_param("nopat", nopat);
@@ -272,7 +274,7 @@ static void pat_ap_init(u64 pat)
wrmsrl(MSR_IA32_CR_PAT, pat);
}
-void init_cache_modes(void)
+void __init init_cache_modes(void)
{
u64 pat = 0;
@@ -313,6 +315,12 @@ void init_cache_modes(void)
*/
pat = PAT(0, WB) | PAT(1, WT) | PAT(2, UC_MINUS) | PAT(3, UC) |
PAT(4, WB) | PAT(5, WT) | PAT(6, UC_MINUS) | PAT(7, UC);
+ } else if (!pat_force_disabled && cpu_feature_enabled(X86_FEATURE_HYPERVISOR)) {
+ /*
+ * Clearly PAT is enabled underneath. Allow pat_enabled() to
+ * reflect this.
+ */
+ pat_bp_enabled = true;
}
__init_cache_modes(pat);