x86/mm/pat: Emulate PAT when it is disabled

[mirror_ubuntu-zesty-kernel.git] / arch / x86 / mm / pat.c

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 476d0780560f2c980dbae99f22ffef113a8bf806..6dc7826e4797fd656ea9c19765c6fac8788ed848 100644 (file)
--- 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);