x86: PAT infrastructure patch

Sets up pat_init() infrastructure.

PAT MSR has following setting.
	PAT
	|PCD
	||PWT
	|||
	000 WB		_PAGE_CACHE_WB
	001 WC		_PAGE_CACHE_WC
	010 UC-		_PAGE_CACHE_UC_MINUS
	011 UC		_PAGE_CACHE_UC

We are effectively changing WT from boot time setting to WC.
UC_MINUS is used to provide backward compatibility to existing /dev/mem
users(X).

reserve_memtype and free_memtype are new interfaces for maintaining alias-free
mapping. It is currently implemented in a simple way with a linked list and
not optimized. reserve and free tracks the effective memory type, as a result
of PAT and MTRR setting rather than what is actually requested in PAT.

pat_init piggy backs on mtrr_init as the rules for setting both pat and mtrr
are same.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 402 insertions, 0 deletions

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
new file mode 100644
index 0000000..7cc71d8
--- /dev/null
+++ b/arch/x86/mm/pat.c
@@ -0,0 +1,402 @@
+/*
+ * Handle caching attributes in page tables (PAT)
+ *
+ * Authors: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
+ *          Suresh B Siddha <suresh.b.siddha@intel.com>
+ *
+ * Loosely based on earlier PAT patchset from Eric Biederman and Andi Kleen.
+ */
+
+#include <linux/mm.h>
+#include <linux/kernel.h>
+#include <linux/gfp.h>
+#include <linux/fs.h>
+
+#include <asm/msr.h>
+#include <asm/tlbflush.h>
+#include <asm/processor.h>
+#include <asm/pgtable.h>
+#include <asm/pat.h>
+#include <asm/e820.h>
+#include <asm/cacheflush.h>
+#include <asm/fcntl.h>
+#include <asm/mtrr.h>
+
+int pat_wc_enabled = 1;
+
+static u64 __read_mostly boot_pat_state;
+
+static int nopat(char *str)
+{
+	pat_wc_enabled = 0;
+	printk(KERN_INFO "x86: PAT support disabled.\n");
+
+	return 0;
+}
+early_param("nopat", nopat);
+
+static int pat_known_cpu(void)
+{
+	if (!pat_wc_enabled)
+		return 0;
+
+	if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
+	    (boot_cpu_data.x86 == 0xF ||
+	     (boot_cpu_data.x86 == 6 && boot_cpu_data.x86_model >= 15))) {
+		if (cpu_has_pat) {
+			return 1;
+		}
+	}
+
+	pat_wc_enabled = 0;
+	printk(KERN_INFO "CPU and/or kernel does not support PAT.\n");
+	return 0;
+}
+
+enum {
+	PAT_UC = 0,		/* uncached */
+	PAT_WC = 1,		/* Write combining */
+	PAT_WT = 4,		/* Write Through */
+	PAT_WP = 5,		/* Write Protected */
+	PAT_WB = 6,		/* Write Back (default) */
+	PAT_UC_MINUS = 7,	/* UC, but can be overriden by MTRR */
+};
+
+#define PAT(x,y)	((u64)PAT_ ## y << ((x)*8))
+
+void pat_init(void)
+{
+	u64 pat;
+
+#ifndef CONFIG_X86_PAT
+	nopat(NULL);
+#endif
+
+	/* Boot CPU enables PAT based on CPU feature */
+	if (!smp_processor_id() && !pat_known_cpu())
+		return;
+
+	/* APs enable PAT iff boot CPU has enabled it before */
+	if (smp_processor_id() && !pat_wc_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);
+
+	/* Boot CPU check */
+	if (!smp_processor_id()) {
+		rdmsrl(MSR_IA32_CR_PAT, boot_pat_state);
+	}
+
+	wrmsrl(MSR_IA32_CR_PAT, pat);
+	printk(KERN_INFO "x86 PAT enabled: cpu %d, old 0x%Lx, new 0x%Lx\n",
+	       smp_processor_id(), boot_pat_state, pat);
+}
+
+#undef PAT
+
+static char *cattr_name(unsigned long flags)
+{
+	switch (flags & _PAGE_CACHE_MASK) {
+		case _PAGE_CACHE_UC:		return "uncached";
+		case _PAGE_CACHE_UC_MINUS:	return "uncached-minus";
+		case _PAGE_CACHE_WB:		return "write-back";
+		case _PAGE_CACHE_WC:		return "write-combining";
+		default:			return "broken";
+	}
+}
+
+/*
+ * The global memtype list keeps track of memory type for specific
+ * physical memory areas. Conflicting memory types in different
+ * mappings can cause CPU cache corruption. To avoid this we keep track.
+ *
+ * The list is sorted based on starting address and can contain multiple
+ * entries for each address (this allows reference counting for overlapping
+ * areas). All the aliases have the same cache attributes of course.
+ * Zero attributes are represented as holes.
+ *
+ * Currently the data structure is a list because the number of mappings
+ * are expected to be relatively small. If this should be a problem
+ * it could be changed to a rbtree or similar.
+ *
+ * memtype_lock protects the whole list.
+ */
+
+struct memtype {
+	u64 start;
+	u64 end;
+	unsigned long type;
+	struct list_head nd;
+};
+
+static LIST_HEAD(memtype_list);
+static DEFINE_SPINLOCK(memtype_lock); 	/* protects memtype list */
+
+/*
+ * Does intersection of PAT memory type and MTRR memory type and returns
+ * the resulting memory type as PAT understands it.
+ * (Type in pat and mtrr will not have same value)
+ * The intersection is based on "Effective Memory Type" tables in IA-32
+ * SDM vol 3a
+ */
+static int pat_x_mtrr_type(u64 start, u64 end, unsigned long prot,
+				unsigned long *ret_prot)
+{
+	unsigned long pat_type;
+	u8 mtrr_type;
+
+	mtrr_type = mtrr_type_lookup(start, end);
+	if (mtrr_type == 0xFF) {		/* MTRR not enabled */
+		*ret_prot = prot;
+		return 0;
+	}
+	if (mtrr_type == 0xFE) {		/* MTRR match error */
+		*ret_prot = _PAGE_CACHE_UC;
+		return -1;
+	}
+	if (mtrr_type != MTRR_TYPE_UNCACHABLE &&
+	    mtrr_type != MTRR_TYPE_WRBACK &&
+	    mtrr_type != MTRR_TYPE_WRCOMB) {	/* MTRR type unhandled */
+		*ret_prot = _PAGE_CACHE_UC;
+		return -1;
+	}
+
+	pat_type = prot & _PAGE_CACHE_MASK;
+	prot &= (~_PAGE_CACHE_MASK);
+
+	/* Currently doing intersection by hand. Optimize it later. */
+	if (pat_type == _PAGE_CACHE_WC) {
+		*ret_prot = prot | _PAGE_CACHE_WC;
+	} else if (pat_type == _PAGE_CACHE_UC_MINUS) {
+		*ret_prot = prot | _PAGE_CACHE_UC_MINUS;
+	} else if (pat_type == _PAGE_CACHE_UC ||
+	           mtrr_type == MTRR_TYPE_UNCACHABLE) {
+		*ret_prot = prot | _PAGE_CACHE_UC;
+	} else if (mtrr_type == MTRR_TYPE_WRCOMB) {
+		*ret_prot = prot | _PAGE_CACHE_WC;
+	} else {
+		*ret_prot = prot | _PAGE_CACHE_WB;
+	}
+
+	return 0;
+}
+
+int reserve_memtype(u64 start, u64 end, unsigned long req_type,
+			unsigned long *ret_type)
+{
+	struct memtype *new_entry = NULL;
+	struct memtype *parse;
+	unsigned long actual_type;
+	int err = 0;
+
+	/* Only track when pat_wc_enabled */
+	if (!pat_wc_enabled) {
+		if (ret_type)
+			*ret_type = req_type;
+
+		return 0;
+	}
+
+	/* Low ISA region is always mapped WB in page table. No need to track */
+	if (start >= ISA_START_ADDRESS && (end - 1) <= ISA_END_ADDRESS) {
+		if (ret_type)
+			*ret_type = _PAGE_CACHE_WB;
+
+		return 0;
+	}
+
+	req_type &= _PAGE_CACHE_MASK;
+	err = pat_x_mtrr_type(start, end, req_type, &actual_type);
+	if (err) {
+		if (ret_type)
+			*ret_type = actual_type;
+
+		return -EINVAL;
+	}
+
+	new_entry  = kmalloc(sizeof(struct memtype), GFP_KERNEL);
+	if (!new_entry)
+		return -ENOMEM;
+
+	new_entry->start = start;
+	new_entry->end = end;
+	new_entry->type = actual_type;
+
+	if (ret_type)
+		*ret_type = actual_type;
+
+	spin_lock(&memtype_lock);
+
+	/* Search for existing mapping that overlaps the current range */
+	list_for_each_entry(parse, &memtype_list, nd) {
+		struct memtype *saved_ptr;
+
+		if (parse->start >= end) {
+			list_add(&new_entry->nd, parse->nd.prev);
+			new_entry = NULL;
+			break;
+		}
+
+		if (start <= parse->start && end >= parse->start) {
+			if (actual_type != parse->type && ret_type) {
+				actual_type = parse->type;
+				*ret_type = actual_type;
+				new_entry->type = actual_type;
+			}
+
+			if (actual_type != parse->type) {
+				printk(
+		KERN_INFO "%s:%d conflicting memory types %Lx-%Lx %s<->%s\n",
+					current->comm, current->pid,
+					start, end,
+					cattr_name(actual_type),
+					cattr_name(parse->type));
+				err = -EBUSY;
+				break;
+			}
+
+			saved_ptr = parse;
+			/*
+			 * Check to see whether the request overlaps more
+			 * than one entry in the list
+			 */
+			list_for_each_entry_continue(parse, &memtype_list, nd) {
+				if (end <= parse->start) {
+					break;
+				}
+
+				if (actual_type != parse->type) {
+					printk(
+		KERN_INFO "%s:%d conflicting memory types %Lx-%Lx %s<->%s\n",
+						current->comm, current->pid,
+						start, end,
+						cattr_name(actual_type),
+						cattr_name(parse->type));
+					err = -EBUSY;
+					break;
+				}
+			}
+
+			if (err) {
+				break;
+			}
+
+			/* No conflict. Go ahead and add this new entry */
+			list_add(&new_entry->nd, saved_ptr->nd.prev);
+			new_entry = NULL;
+			break;
+		}
+
+		if (start < parse->end) {
+			if (actual_type != parse->type && ret_type) {
+				actual_type = parse->type;
+				*ret_type = actual_type;
+				new_entry->type = actual_type;
+			}
+
+			if (actual_type != parse->type) {
+				printk(
+		KERN_INFO "%s:%d conflicting memory types %Lx-%Lx %s<->%s\n",
+					current->comm, current->pid,
+					start, end,
+					cattr_name(actual_type),
+					cattr_name(parse->type));
+				err = -EBUSY;
+				break;
+			}
+
+			saved_ptr = parse;
+			/*
+			 * Check to see whether the request overlaps more
+			 * than one entry in the list
+			 */
+			list_for_each_entry_continue(parse, &memtype_list, nd) {
+				if (end <= parse->start) {
+					break;
+				}
+
+				if (actual_type != parse->type) {
+					printk(
+		KERN_INFO "%s:%d conflicting memory types %Lx-%Lx %s<->%s\n",
+						current->comm, current->pid,
+						start, end,
+						cattr_name(actual_type),
+						cattr_name(parse->type));
+					err = -EBUSY;
+					break;
+				}
+			}
+
+			if (err) {
+				break;
+			}
+
+			/* No conflict. Go ahead and add this new entry */
+			list_add(&new_entry->nd, &saved_ptr->nd);
+			new_entry = NULL;
+			break;
+		}
+	}
+
+	if (err) {
+		kfree(new_entry);
+		spin_unlock(&memtype_lock);
+		return err;
+	}
+
+	if (new_entry) {
+		/* No conflict. Not yet added to the list. Add to the tail */
+		list_add_tail(&new_entry->nd, &memtype_list);
+	}
+
+	spin_unlock(&memtype_lock);
+	return err;
+}
+
+int free_memtype(u64 start, u64 end)
+{
+	struct memtype *ml;
+	int err = -EINVAL;
+
+	/* Only track when pat_wc_enabled */
+	if (!pat_wc_enabled) {
+		return 0;
+	}
+
+	/* Low ISA region is always mapped WB. No need to track */
+	if (start >= ISA_START_ADDRESS && end <= ISA_END_ADDRESS) {
+		return 0;
+	}
+
+	spin_lock(&memtype_lock);
+	list_for_each_entry(ml, &memtype_list, nd) {
+		if (ml->start == start && ml->end == end) {
+			list_del(&ml->nd);
+			kfree(ml);
+			err = 0;
+			break;
+		}
+	}
+	spin_unlock(&memtype_lock);
+
+	if (err) {
+		printk(KERN_DEBUG "%s:%d freeing invalid memtype %Lx-%Lx\n",
+			current->comm, current->pid, start, end);
+	}
+	return err;
+}
+