Commit-ID: d79a40caf8e15a2a15ecdefdc9d05865d4f37baa Gitweb: http://git.kernel.org/tip/d79a40caf8e15a2a15ecdefdc9d05865d4f37baa Author: Toshi Kani <toshi.kani@xxxxxx> AuthorDate: Thu, 4 Jun 2015 18:55:12 +0200 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitDate: Sun, 7 Jun 2015 15:28:54 +0200 x86/mm/pat: Use 7th PAT MSR slot for Write-Through PAT type Assign Write-Through type to the PA7 slot in the PAT MSR when the processor is not affected by PAT errata. The PA7 slot is chosen to improve robustness in the presence of errata that might cause the high PAT bit to be ignored. This way a buggy PA7 slot access will hit the PA3 slot, which is UC, so at worst we lose performance without causing a correctness issue. The following Intel processors are affected by the PAT errata. Errata CPUID ---------------------------------------------------- Pentium 2, A52 family 0x6, model 0x5 Pentium 3, E27 family 0x6, model 0x7, 0x8 Pentium 3 Xenon, G26 family 0x6, model 0x7, 0x8, 0xa Pentium M, Y26 family 0x6, model 0x9 Pentium M 90nm, X9 family 0x6, model 0xd Pentium 4, N46 family 0xf, model 0x0 Instead of making sharp boundary checks, we remain conservative and exclude all Pentium 2, 3, M and 4 family processors. For those, _PAGE_CACHE_MODE_WT is redirected to UC- per the default setup in __cachemode2pte_tbl[]. Signed-off-by: Toshi Kani <toshi.kani@xxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx> Cc: Elliott@xxxxxx Cc: H. Peter Anvin <hpa@xxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Luis R. Rodriguez <mcgrof@xxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: arnd@xxxxxxxx Cc: hch@xxxxxx Cc: hmh@xxxxxxxxxx Cc: jgross@xxxxxxxx Cc: konrad.wilk@xxxxxxxxxx Cc: linux-mm <linux-mm@xxxxxxxxx> Cc: linux-nvdimm@xxxxxxxxxxxx Cc: stefan.bader@xxxxxxxxxxxxx Cc: yigal@xxxxxxxxxxxxx Link: https://lkml.kernel.org/r/1433187393-22688-2-git-send-email-toshi.kani@xxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> --- arch/x86/mm/pat.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++--------- 1 file changed, 50 insertions(+), 9 deletions(-) diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c index f89e460..59ab1a0f 100644 --- a/arch/x86/mm/pat.c +++ b/arch/x86/mm/pat.c @@ -235,6 +235,7 @@ static void pat_ap_init(u64 pat) void pat_init(void) { u64 pat; + struct cpuinfo_x86 *c = &boot_cpu_data; if (!pat_enabled()) { /* @@ -244,7 +245,7 @@ void pat_init(void) * 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: + * PTE encoding: * * PCD * |PWT PAT @@ -259,21 +260,61 @@ 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); - } else { + + } else if ((c->x86_vendor == X86_VENDOR_INTEL) && + (((c->x86 == 0x6) && (c->x86_model <= 0xd)) || + ((c->x86 == 0xf) && (c->x86_model <= 0x6)))) { /* - * PTE encoding used in Linux: + * PAT support with the lower four entries. Intel Pentium 2, + * 3, M, and 4 are affected by PAT errata, which makes the + * upper four entries unusable. To be on the safe side, we don't + * use those. + * + * PTE encoding: * PAT * |PCD - * ||PWT - * ||| - * 000 WB _PAGE_CACHE_WB - * 001 WC _PAGE_CACHE_WC - * 010 UC- _PAGE_CACHE_UC_MINUS - * 011 UC _PAGE_CACHE_UC + * ||PWT PAT + * ||| slot + * 000 0 WB : _PAGE_CACHE_MODE_WB + * 001 1 WC : _PAGE_CACHE_MODE_WC + * 010 2 UC-: _PAGE_CACHE_MODE_UC_MINUS + * 011 3 UC : _PAGE_CACHE_MODE_UC * PAT bit unused + * + * NOTE: When WT or WP is used, it is redirected to UC- per + * the default setup in __cachemode2pte_tbl[]. */ 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); + } else { + /* + * Full PAT support. We put WT in slot 7 to improve + * robustness in the presence of errata that might cause + * the high PAT bit to be ignored. This way, a buggy slot 7 + * access will hit slot 3, and slot 3 is UC, so at worst + * we lose performance without causing a correctness issue. + * Pentium 4 erratum N46 is an example for such an erratum, + * although we try not to use PAT at all on affected CPUs. + * + * PTE encoding: + * PAT + * |PCD + * ||PWT PAT + * ||| slot + * 000 0 WB : _PAGE_CACHE_MODE_WB + * 001 1 WC : _PAGE_CACHE_MODE_WC + * 010 2 UC-: _PAGE_CACHE_MODE_UC_MINUS + * 011 3 UC : _PAGE_CACHE_MODE_UC + * 100 4 WB : Reserved + * 101 5 WC : Reserved + * 110 6 UC-: Reserved + * 111 7 WT : _PAGE_CACHE_MODE_WT + * + * The reserved slots are unused, but mapped to their + * corresponding types in the presence of PAT errata. + */ + 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, WT); } if (!boot_cpu_done) { -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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