[PATCH 02/20] x86/mm/pat: Emulate PAT when it is disabled

Borislav Petkov
2015-06-04T16:55:54Z

From: Borislav Petkov <bp@suse.de>

In the case when PAT is disabled on the command line with "nopat" or
when virtualization doesn't support PAT (correctly) - see

9d34cfdf4796 ("x86: Don't rely on VMWare emulating PAT MSR correctly").

we emulate it using the PWT and PCD cache attribute bits. Get rid of
boot_pat_state while at it.

Based on a conglomerate patch from Toshi Kani.

Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Toshi Kani <toshi.kani@hp.com>
Acked-by: Juergen Gross <jgross@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: arnd@arndb.de
Cc: Elliott@hp.com
Cc: hch@lst.de
Cc: hmh@hmh.eng.br
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: konrad.wilk@oracle.com
Cc: linux-mm <linux-mm@kvack.org>
Cc: linux-nvdimm@lists.01.org
Cc: Luis R. Rodriguez <mcgrof@suse.com>
Cc: stefan.bader@canonical.com
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Cc: yigal@plexistor.com
---
arch/x86/include/asm/pat.h | 2 +-
arch/x86/mm/init.c | 6 ++--
arch/x86/mm/pat.c | 81 ++++++++++++++++++++++++++++++----------------
arch/x86/xen/enlighten.c | 5 +--
4 files changed, 60 insertions(+), 34 deletions(-)

diff --git a/arch/x86/include/asm/pat.h b/arch/x86/include/asm/pat.h
index cdcff7f7f694..ca6c228d5e62 100644
--- a/arch/x86/include/asm/pat.h
+++ b/arch/x86/include/asm/pat.h
@@ -6,7 +6,7 @@

bool pat_enabled(void);
extern void pat_init(void);
-void pat_init_cache_modes(void);
+void pat_init_cache_modes(u64);

extern int reserve_memtype(u64 start, u64 end,
enum page_cache_mode req_pcm, enum page_cache_mode *ret_pcm);
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 1d553186c434..8533b46e6bee 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -40,7 +40,7 @@
*/
uint16_t __cachemode2pte_tbl[_PAGE_CACHE_MODE_NUM] = {
[_PAGE_CACHE_MODE_WB ] = 0 | 0 ,
- [_PAGE_CACHE_MODE_WC ] = _PAGE_PWT | 0 ,
+ [_PAGE_CACHE_MODE_WC ] = 0 | _PAGE_PCD,
[_PAGE_CACHE_MODE_UC_MINUS] = 0 | _PAGE_PCD,
[_PAGE_CACHE_MODE_UC ] = _PAGE_PWT | _PAGE_PCD,
[_PAGE_CACHE_MODE_WT ] = 0 | _PAGE_PCD,
@@ -50,11 +50,11 @@ EXPORT_SYMBOL(__cachemode2pte_tbl);

uint8_t __pte2cachemode_tbl[8] = {
[__pte2cm_idx( 0 | 0 | 0 )] = _PAGE_CACHE_MODE_WB,
- [__pte2cm_idx(_PAGE_PWT | 0 | 0 )] = _PAGE_CACHE_MODE_WC,
+ [__pte2cm_idx(_PAGE_PWT | 0 | 0 )] = _PAGE_CACHE_MODE_UC_MINUS,
[__pte2cm_idx( 0 | _PAGE_PCD | 0 )] = _PAGE_CACHE_MODE_UC_MINUS,
[__pte2cm_idx(_PAGE_PWT | _PAGE_PCD | 0 )] = _PAGE_CACHE_MODE_UC,
[__pte2cm_idx( 0 | 0 | _PAGE_PAT)] = _PAGE_CACHE_MODE_WB,
- [__pte2cm_idx(_PAGE_PWT | 0 | _PAGE_PAT)] = _PAGE_CACHE_MODE_WC,
+ [__pte2cm_idx(_PAGE_PWT | 0 | _PAGE_PAT)] = _PAGE_CACHE_MODE_UC_MINUS,
[__pte2cm_idx(0 | _PAGE_PCD | _PAGE_PAT)] = _PAGE_CACHE_MODE_UC_MINUS,
[__pte2cm_idx(_PAGE_PWT | _PAGE_PCD | _PAGE_PAT)] = _PAGE_CACHE_MODE_UC,
};
diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 476d0780560f..6dc7826e4797 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -68,8 +68,6 @@ static int __init pat_debug_setup(char *str)
}
__setup("debugpat", pat_debug_setup);

-static u64 __read_mostly boot_pat_state;
-
#ifdef CONFIG_X86_PAT
/*
* X86 PAT uses page flags WC and Uncached together to keep track of
@@ -177,14 +175,12 @@ static enum page_cache_mode pat_get_cache_mode(unsigned pat_val, char *msg)
* configuration.
* Using lower indices is preferred, so we start with highest index.
*/
-void pat_init_cache_modes(void)
+void pat_init_cache_modes(u64 pat)
{
- int i;
enum page_cache_mode cache;
char pat_msg[33];
- u64 pat;
+ int i;

- rdmsrl(MSR_IA32_CR_PAT, pat);
pat_msg[32] = 0;
for (i = 7; i >= 0; i--) {
cache = pat_get_cache_mode((pat >> (i * 8)) & 7,
@@ -198,24 +194,33 @@ void pat_init_cache_modes(void)

static void pat_bsp_init(u64 pat)
{
+ u64 tmp_pat;
+
if (!cpu_has_pat) {
pat_disable("PAT not supported by CPU.");
return;
}

- rdmsrl(MSR_IA32_CR_PAT, boot_pat_state);
- if (!boot_pat_state) {
+ if (!pat_enabled())
+ goto done;
+
+ rdmsrl(MSR_IA32_CR_PAT, tmp_pat);
+ if (!tmp_pat) {
pat_disable("PAT MSR is 0, disabled.");
return;
}

wrmsrl(MSR_IA32_CR_PAT, pat);

- pat_init_cache_modes();
+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
@@ -231,25 +236,45 @@ void pat_init(void)
{
u64 pat;

- if (!pat_enabled())
- return;
-
- /*
- * Set PWT to Write-Combining. All other bits stay the same:
- *
- * PTE encoding used in Linux:
- * PAT
- * |PCD
- * ||PWT
- * |||
- * 000 WB _PAGE_CACHE_WB
- * 001 WC _PAGE_CACHE_WC
- * 010 UC- _PAGE_CACHE_UC_MINUS
- * 011 UC _PAGE_CACHE_UC
- * PAT bit unused
- */
- pat = PAT(0, WB) | PAT(1, WC) | PAT(2, UC_MINUS) | PAT(3, UC) |
- PAT(4, WB) | PAT(5, WC) | PAT(6, UC_MINUS) | PAT(7, UC);
+ if (!pat_enabled()) {
+ /*
+ * 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.
+ *
+ * PTE encoding used:
+ *
+ * PCD
+ * |PWT PAT
+ * || slot
+ * 00 0 WB : _PAGE_CACHE_MODE_WB
+ * 01 1 WT : _PAGE_CACHE_MODE_WT
+ * 10 2 UC-: _PAGE_CACHE_MODE_UC_MINUS
+ * 11 3 UC : _PAGE_CACHE_MODE_UC
+ *
+ * NOTE: When WC or WP is used, it is redirected to UC- per
+ * the default setup in __cachemode2pte_tbl[].
+ */
+ 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 {
+ /*
+ * PTE encoding used in Linux:
+ * PAT
+ * |PCD
+ * ||PWT
+ * |||
+ * 000 WB _PAGE_CACHE_WB
+ * 001 WC _PAGE_CACHE_WC
+ * 010 UC- _PAGE_CACHE_UC_MINUS
+ * 011 UC _PAGE_CACHE_UC
+ * PAT bit unused
+ */
+ pat = PAT(0, WB) | PAT(1, WC) | PAT(2, UC_MINUS) | PAT(3, UC) |
+ PAT(4, WB) | PAT(5, WC) | PAT(6, UC_MINUS) | PAT(7, UC);
+ }

if (!boot_cpu_done) {
pat_bsp_init(pat);
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 46957ead3060..53233a9beea9 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1467,6 +1467,7 @@ asmlinkage __visible void __init xen_start_kernel(void)
{
struct physdev_set_iopl set_iopl;
unsigned long initrd_start = 0;
+ u64 pat;
int rc;

if (!xen_start_info)
@@ -1574,8 +1575,8 @@ asmlinkage __visible void __init xen_start_kernel(void)
* Modify the cache mode translation tables to match Xen's PAT
* configuration.
*/
-
- pat_init_cache_modes();
+ rdmsrl(MSR_IA32_CR_PAT, pat);
+ pat_init_cache_modes(pat);

/* keep using Xen gdt for now; no urgent need to change it */

--
2.3.5