This is a note to let you know that I've just added the patch titled
x86/PAT: Have pat_enabled() properly reflect state when running on Xen
to the 5.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-pat-have-pat_enabled-properly-reflect-state-when-running-on-xen.patch
and it can be found in the queue-5.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 72cbc8f04fe2fa93443c0fcccb7ad91dfea3d9ce Mon Sep 17 00:00:00 2001
From: Jan Beulich <jbeulich@xxxxxxxx>
Date: Thu, 28 Apr 2022 16:50:29 +0200
Subject: x86/PAT: Have pat_enabled() properly reflect state when running on Xen
From: Jan Beulich <jbeulich@xxxxxxxx>
commit 72cbc8f04fe2fa93443c0fcccb7ad91dfea3d9ce upstream.
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@xxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Acked-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
Link: https://lore.kernel.org/r/9385fa60-fa5d-f559-a137-6608408f88b0@xxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/mm/pat/memtype.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
--- 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);
Patches currently in stable-queue which might be from jbeulich@xxxxxxxx are
queue-5.19/xen-privcmd-fix-error-exit-of-privcmd_ioctl_dm_op.patch
queue-5.19/x86-pat-have-pat_enabled-properly-reflect-state-when-running-on-xen.patch
queue-5.19/x86-entry-fix-entry_int80_compat-for-xen-pv-guests.patch
