From: Jan Beulich <jbeulich@suse.com>
To: Andrew Lutomirski <luto@kernel.org>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>
Cc: lkml <linux-kernel@vger.kernel.org>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Subject: [PATCH] x86/PAT: have pat_enabled() properly reflect state when running on e.g. Xen
Date: Thu, 28 Apr 2022 16:50:29 +0200 [thread overview]
Message-ID: <9385fa60-fa5d-f559-a137-6608408f88b0@suse.com> (raw)
The latest with commit bdd8b6c98239 ("drm/i915: replace X86_FEATURE_PAT
with pat_enabled()") pat_enabled() returning false (because of PAT
initialization being suppressed in the absence of MTRRs being announced
to be available) 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
performant 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).
Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
On the system where I observed the issue, a knock-on effect of driver
initialization failing was that the SATA-controller also started to
report failures.
--- 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 +315,13 @@ 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 &&
+ boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
+ /*
+ * Clearly PAT is enabled underneath. Allow pat_enabled() to
+ * reflect this.
+ */
+ pat_bp_enabled = true;
}
__init_cache_modes(pat);
next reply other threads:[~2022-04-28 14:50 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-28 14:50 Jan Beulich [this message]
2022-05-03 12:54 ` [PATCH] x86/PAT: have pat_enabled() properly reflect state when running on e.g. Xen Juergen Gross
2022-05-11 13:32 ` Juergen Gross
2022-05-21 13:56 ` Chuck Zmudzinski
2022-05-25 8:55 ` Ping: " Jan Beulich
2022-07-04 11:58 ` Thorsten Leemhuis
2022-07-04 12:26 ` Jan Beulich
2022-07-05 10:57 ` Thorsten Leemhuis
2022-07-05 11:02 ` Jan Beulich
2022-07-05 13:36 ` Borislav Petkov
2022-07-05 13:38 ` Juergen Gross
2022-07-14 17:17 ` Chuck Zmudzinski
2022-07-14 22:33 ` Chuck Zmudzinski
2022-07-14 22:45 ` Chuck Zmudzinski
2022-07-19 14:26 ` Chuck Zmudzinski
2022-07-05 15:04 ` Borislav Petkov
2022-07-05 15:56 ` Jan Beulich
2022-07-05 16:14 ` Borislav Petkov
2022-07-06 6:17 ` Jan Beulich
2022-07-06 17:01 ` Borislav Petkov
2022-07-07 6:38 ` Jan Beulich
2022-07-11 10:40 ` Borislav Petkov
2022-07-11 11:38 ` Chuck Zmudzinski
2022-07-11 12:28 ` [PATCH] x86/PAT: have pat_enabled() properly reflect state when running on e.g. Xen, with corrected patch Chuck Zmudzinski
2022-07-11 14:18 ` [PATCH] x86/PAT: have pat_enabled() properly reflect state when running on e.g. Xen Chuck Zmudzinski
2022-07-11 14:31 ` Juergen Gross
2022-07-11 17:41 ` Chuck Zmudzinski
2022-07-12 5:49 ` Juergen Gross
2022-07-12 6:04 ` Jan Beulich
2022-07-12 13:22 ` Chuck Zmudzinski
2022-07-12 13:32 ` Juergen Gross
2022-07-12 15:09 ` Chuck Zmudzinski
2022-07-12 15:30 ` Juergen Gross
2022-07-12 16:34 ` Chuck Zmudzinski
2022-08-15 10:20 ` [tip: x86/urgent] x86/PAT: Have pat_enabled() properly reflect state when running on Xen tip-bot2 for Jan Beulich
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