[PATCH v4 7/7] mtrr, mm, x86: Enhance MTRR checks for KVA huge page mapping

Toshi Kani
2015-03-24T22:28:03Z

This patch adds an additional argument, 'uniform', to
mtrr_type_lookup(), which returns 1 when a given range is
covered uniformly by MTRRs, i.e. the range is fully covered
by a single MTRR entry or the default type.

pud_set_huge() and pmd_set_huge() are changed to check the
new 'uniform' flag to see if it is safe to create a huge page
mapping to the range. This allows them to create a huge page
mapping to a range covered by a single MTRR entry of any
memory type. It also detects a non-optimal request properly.
They continue to check with the WB type since the WB type has
no effect even if a request spans multiple MTRR entries.

pmd_set_huge() logs a warning message to a non-optimal request
so that driver writers will be aware of such a case. Drivers
should make a mapping request aligned to a single MTRR entry
when the range is covered by MTRRs.

Signed-off-by: Toshi Kani <toshi.kani@hp.com>
---
arch/x86/include/asm/mtrr.h | 5 +++--
arch/x86/kernel/cpu/mtrr/generic.c | 35 +++++++++++++++++++++++++++--------
arch/x86/mm/pat.c | 4 ++--
arch/x86/mm/pgtable.c | 25 +++++++++++++++----------
4 files changed, 47 insertions(+), 22 deletions(-)

diff --git a/arch/x86/include/asm/mtrr.h b/arch/x86/include/asm/mtrr.h
index a174af6..da8dff1 100644
--- a/arch/x86/include/asm/mtrr.h
+++ b/arch/x86/include/asm/mtrr.h
@@ -31,7 +31,7 @@
* arch_phys_wc_add and arch_phys_wc_del.
*/
# ifdef CONFIG_MTRR
-extern u8 mtrr_type_lookup(u64 addr, u64 end);
+extern u8 mtrr_type_lookup(u64 addr, u64 end, u8 *uniform);
extern void mtrr_save_fixed_ranges(void *);
extern void mtrr_save_state(void);
extern int mtrr_add(unsigned long base, unsigned long size,
@@ -50,11 +50,12 @@ extern int mtrr_trim_uncached_memory(unsigned long end_pfn);
extern int amd_special_default_mtrr(void);
extern int phys_wc_to_mtrr_index(int handle);
# else
-static inline u8 mtrr_type_lookup(u64 addr, u64 end)
+static inline u8 mtrr_type_lookup(u64 addr, u64 end, u8 *uniform)
{
/*
* Return no-MTRRs:
*/
+ *uniform = 1;
return MTRR_TYPE_INVALID;
}
#define mtrr_save_fixed_ranges(arg) do {} while (0)
diff --git a/arch/x86/kernel/cpu/mtrr/generic.c b/arch/x86/kernel/cpu/mtrr/generic.c
index 3652e2b..a83f27a 100644
--- a/arch/x86/kernel/cpu/mtrr/generic.c
+++ b/arch/x86/kernel/cpu/mtrr/generic.c
@@ -148,19 +148,22 @@ static u8 mtrr_type_lookup_fixed(u64 start, u64 end)
* Return Value:
* MTRR_TYPE_(type) - Matched memory type or default memory type (unmatched)
*
- * Output Argument:
+ * Output Arguments:
* repeat - Set to 1 when [start:end] spanned across MTRR range and type
* returned corresponds only to [start:*partial_end]. Caller has
* to lookup again for [*partial_end:end].
+ * uniform - Set to 1 when MTRR covers the region uniformly, i.e. the region
+ * is fully covered by a single MTRR entry or the default type.
*/
static u8 mtrr_type_lookup_variable(u64 start, u64 end, u64 *partial_end,
- int *repeat)
+ int *repeat, u8 *uniform)
{
int i;
u64 base, mask;
u8 prev_match, curr_match;

*repeat = 0;
+ *uniform = 1;

/* Make end inclusive end, instead of exclusive */
end--;
@@ -208,6 +211,7 @@ static u8 mtrr_type_lookup_variable(u64 start, u64 end, u64 *partial_end,

end = *partial_end - 1; /* end is inclusive */
*repeat = 1;
+ *uniform = 0;
}

if (!start_state)
@@ -219,6 +223,7 @@ static u8 mtrr_type_lookup_variable(u64 start, u64 end, u64 *partial_end,
continue;
}

+ *uniform = 0;
if (check_type_overlap(&prev_match, &curr_match))
return curr_match;
}
@@ -235,13 +240,19 @@ static u8 mtrr_type_lookup_variable(u64 start, u64 end, u64 *partial_end,
* Return Values:
* MTRR_TYPE_(type) - The effective MTRR type for the region
* MTRR_TYPE_INVALID - MTRR is disabled
+ *
+ * Output Argument:
+ * uniform - Set to 1 when MTRR covers the region uniformly, i.e. the region
+ * is fully covered by a single MTRR entry or the default type.
*/
-u8 mtrr_type_lookup(u64 start, u64 end)
+u8 mtrr_type_lookup(u64 start, u64 end, u8 *uniform)
{
- u8 type, prev_type;
+ u8 type, prev_type, is_uniform, dummy;
int repeat;
u64 partial_end;

+ *uniform = 1;
+
if (!mtrr_state_set)
return MTRR_TYPE_INVALID;

@@ -253,14 +264,17 @@ u8 mtrr_type_lookup(u64 start, u64 end)
* the variable ranges.
*/
type = mtrr_type_lookup_fixed(start, end);
- if (type != MTRR_TYPE_INVALID)
+ if (type != MTRR_TYPE_INVALID) {
+ *uniform = 0;
return type;
+ }

/*
* Look up the variable ranges. Look of multiple ranges matching
* this address and pick type as per MTRR precedence.
*/
- type = mtrr_type_lookup_variable(start, end, &partial_end, &repeat);
+ type = mtrr_type_lookup_variable(start, end, &partial_end,
+ &repeat, &is_uniform);

/*
* Common path is with repeat = 0.
@@ -271,16 +285,21 @@ u8 mtrr_type_lookup(u64 start, u64 end)
while (repeat) {
prev_type = type;
start = partial_end;
+ is_uniform = 0;
+
type = mtrr_type_lookup_variable(start, end, &partial_end,
- &repeat);
+ &repeat, &dummy);

- if (check_type_overlap(&prev_type, &type))
+ if (check_type_overlap(&prev_type, &type)) {
+ *uniform = 0;
return type;
+ }
}

if (mtrr_tom2 && (start >= (1ULL<<32)) && (end < mtrr_tom2))
return MTRR_TYPE_WRBACK;

+ *uniform = is_uniform;
return type;
}

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 35af677..372ad42 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -267,9 +267,9 @@ static unsigned long pat_x_mtrr_type(u64 start, u64 end,
* request is for WB.
*/
if (req_type == _PAGE_CACHE_MODE_WB) {
- u8 mtrr_type;
+ u8 mtrr_type, uniform;

- mtrr_type = mtrr_type_lookup(start, end);
+ mtrr_type = mtrr_type_lookup(start, end, &uniform);
if (mtrr_type != MTRR_TYPE_WRBACK)
return _PAGE_CACHE_MODE_UC_MINUS;

diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index cfca4cf..3d6edea 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -567,17 +567,18 @@ void native_set_fixmap(enum fixed_addresses idx, phys_addr_t phys,
* pud_set_huge - setup kernel PUD mapping
*
* MTRR can override PAT memory types with 4KB granularity. Therefore,
- * it does not set up a huge page when the range is covered by a non-WB
- * type of MTRR. MTRR_TYPE_INVALID indicates that MTRR are disabled.
+ * it only sets up a huge page when the range is mapped uniformly by MTRR
+ * (i.e. the range is fully covered by a single MTRR entry or the default
+ * type) or the MTRR memory type is WB.
*
* Return 1 on success, and 0 when no PUD was set.
*/
int pud_set_huge(pud_t *pud, phys_addr_t addr, pgprot_t prot)
{
- u8 mtrr;
+ u8 mtrr, uniform;

- mtrr = mtrr_type_lookup(addr, addr + PUD_SIZE);
- if ((mtrr != MTRR_TYPE_WRBACK) && (mtrr != MTRR_TYPE_INVALID))
+ mtrr = mtrr_type_lookup(addr, addr + PUD_SIZE, &uniform);
+ if ((!uniform) && (mtrr != MTRR_TYPE_WRBACK))
return 0;

prot = pgprot_4k_2_large(prot);
@@ -593,18 +594,22 @@ int pud_set_huge(pud_t *pud, phys_addr_t addr, pgprot_t prot)
* pmd_set_huge - setup kernel PMD mapping
*
* MTRR can override PAT memory types with 4KB granularity. Therefore,
- * it does not set up a huge page when the range is covered by a non-WB
- * type of MTRR. MTRR_TYPE_INVALID indicates that MTRR are disabled.
+ * it only sets up a huge page when the range is mapped uniformly by MTRR
+ * (i.e. the range is fully covered by a single MTRR entry or the default
+ * type) or the MTRR memory type is WB.
*
* Return 1 on success, and 0 when no PMD was set.
*/
int pmd_set_huge(pmd_t *pmd, phys_addr_t addr, pgprot_t prot)
{
- u8 mtrr;
+ u8 mtrr, uniform;

- mtrr = mtrr_type_lookup(addr, addr + PMD_SIZE);
- if ((mtrr != MTRR_TYPE_WRBACK) && (mtrr != MTRR_TYPE_INVALID))
+ mtrr = mtrr_type_lookup(addr, addr + PMD_SIZE, &uniform);
+ if ((!uniform) && (mtrr != MTRR_TYPE_WRBACK)) {
+ pr_warn("pmd_set_huge: requesting [mem %#010llx-%#010llx], which spans more than a single MTRR entry\n",
+ addr, addr + PMD_SIZE);
return 0;
+ }

prot = pgprot_4k_2_large(prot);