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Date: Wed, 16 Mar 2016 18:44:57 -0600
From: Toshi Kani <toshi.kani@....com>
To: mingo@...nel.org, bp@...e.de, hpa@...or.com, tglx@...utronix.de
Cc: mcgrof@...e.com, jgross@...e.com, paul.gortmaker@...driver.com,
konrad.wilk@...cle.com, elliott@....com, x86@...nel.org,
xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
Toshi Kani <toshi.kani@....com>
Subject: [PATCH v2 1/6] x86/mm/pat: Change PAT to support non-default PAT MSR
In preparation to fix a regression caused by 'commit 9cd25aac1f44
("x86/mm/pat: Emulate PAT when it is disabled")', PAT needs to
support a case that PAT MSR is initialized with a non-default
value.
When pat_init() is called in PAT disable state, it initializes
PAT table with the BIOS default value. Xen, however, sets PAT MSR
with a non-default value to enable WC. This causes inconsistency
between PAT table and PAT MSR when PAT is set to disable on Xen.
Change pat_init() to handle the PAT disable cases properly. Add
pat_keep_handoff_state() to handle two cases when PAT is set to
disable.
1. CPU supports PAT: Set PAT table to be consistent with PAT MSR.
2. CPU does not support PAT: Set PAT table to be consistent with
PWT and PCD bits in a PTE.
Signed-off-by: Toshi Kani <toshi.kani@....com>
Cc: Borislav Petkov <bp@...e.de>
Cc: Luis R. Rodriguez <mcgrof@...e.com>
Cc: Juergen Gross <jgross@...e.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
---
arch/x86/mm/pat.c | 80 +++++++++++++++++++++++++++++++++++++++++------------
1 file changed, 62 insertions(+), 18 deletions(-)
diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 04e2e71..e0a34b0 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -207,9 +207,6 @@ static void pat_bsp_init(u64 pat)
return;
}
- if (!pat_enabled())
- goto done;
-
rdmsrl(MSR_IA32_CR_PAT, tmp_pat);
if (!tmp_pat) {
pat_disable("PAT MSR is 0, disabled.");
@@ -218,15 +215,11 @@ static void pat_bsp_init(u64 pat)
wrmsrl(MSR_IA32_CR_PAT, pat);
-done:
pat_init_cache_modes(pat);
}
static void pat_ap_init(u64 pat)
{
- if (!pat_enabled())
- return;
-
if (!cpu_has_pat) {
/*
* If this happens we are on a secondary CPU, but switched to
@@ -238,18 +231,43 @@ static void pat_ap_init(u64 pat)
wrmsrl(MSR_IA32_CR_PAT, pat);
}
-void pat_init(void)
+/**
+ * pat_keep_handoff_state - Set PAT table to the handoff state
+ *
+ * This function keeps PAT in the BIOS handoff state. When CPU supports
+ * PAT, it sets PAT table to be consistent with PAT MSR. When CPU does not
+ * support PAT, it emulates PAT by setting PAT table consistent with PWT
+ * and PCD bits in a PTE.
+ *
+ * The PAT table is global to all CPUs, which is initialized once at
+ * boot-time. Any subsequent calls to this function have no effect.
+ */
+static void pat_keep_handoff_state(void)
{
- u64 pat;
- struct cpuinfo_x86 *c = &boot_cpu_data;
+ u64 pat = 0;
+ static int set_handoff_done;
- if (!pat_enabled()) {
+ if (set_handoff_done)
+ return;
+
+ if (boot_cpu_has(X86_FEATURE_PAT)) {
+ /*
+ * CPU supports PAT. Set PAT table to be consistent with
+ * PAT MSR. This case supports "nopat" boot option, and
+ * virtual machine environments which support PAT without
+ * MTRR. In specific, Xen has unique setup to PAT MSR.
+ *
+ * If PAT MSR returns 0, it is considered invalid and emulates
+ * as No PAT.
+ */
+ rdmsrl(MSR_IA32_CR_PAT, pat);
+ }
+
+ if (!pat) {
/*
* No PAT. Emulate the PAT table that corresponds to the two
- * cache bits, PWT (Write Through) and PCD (Cache Disable). This
- * setup is the same as the BIOS default setup when the system
- * has PAT but the "nopat" boot option has been specified. This
- * emulated PAT table is used when MSR_IA32_CR_PAT returns 0.
+ * cache bits, PWT (Write Through) and PCD (Cache Disable).
+ * This setup is also the same as the BIOS default setup.
*
* PTE encoding:
*
@@ -266,10 +284,36 @@ void pat_init(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);
+ }
+
+ pat_init_cache_modes(pat);
+
+ set_handoff_done = 1;
+}
+
+/**
+ * pat_init - Initialize PAT MSR and PAT table
+ *
+ * This function initializes PAT MSR and PAT table with an OS-defined value
+ * to enable additional cache attributes, WC and WT.
+ *
+ * This function must be called on all CPUs with the specific sequence of
+ * operations defined in Intel SDM. mtrr_rendezvous_handler() provides this
+ * procedure for PAT.
+ */
+void pat_init(void)
+{
+ u64 pat;
+ struct cpuinfo_x86 *c = &boot_cpu_data;
+
+ if (!pat_enabled()) {
+ pat_keep_handoff_state();
+ return;
+ }
- } else if ((c->x86_vendor == X86_VENDOR_INTEL) &&
- (((c->x86 == 0x6) && (c->x86_model <= 0xd)) ||
- ((c->x86 == 0xf) && (c->x86_model <= 0x6)))) {
+ if ((c->x86_vendor == X86_VENDOR_INTEL) &&
+ (((c->x86 == 0x6) && (c->x86_model <= 0xd)) ||
+ ((c->x86 == 0xf) && (c->x86_model <= 0x6)))) {
/*
* PAT support with the lower four entries. Intel Pentium 2,
* 3, M, and 4 are affected by PAT errata, which makes the
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