> - /* 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 I think having this nice picture would be beneficial to folks who want to understand it. And now you can of course expand it with the slot 7 usage. > - * 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 ((c->x86_vendor == X86_VENDOR_INTEL) && > + (((c->x86 == 0x6) && (c->x86_model <= 0xd)) || > + ((c->x86 == 0xf) && (c->x86_model <= 0x6)))) { > + /* > + * Intel Pentium 2, 3, M, and 4 are affected by PAT errata, > + * which makes the upper four entries unusable. We do not > + * use the upper four entries for all the affected processor > + * families for safe. > + * > + * PAT 0:WB, 1:WC, 2:UC-, 3:UC, 4-7:unusable > + * > + * 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 { > + /* > + * WT is set to slot 7, which minimizes the risk of using You say slot 7 here, but the title of the patch says slot 4? > + * the PAT bit as slot 3 is UC and is currently unused. > + * Slot 4 should remain as reserved. > + * > + * PAT 0:WB, 1:WC, 2:UC-, 3:UC, 4-6:reserved, 7:WT > + */ > + 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); > + } > > /* Boot CPU check */ > if (!boot_pat_state) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>