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Subject[PATCH v11 10/12] x86, mm, asm: Add WT support to set_page_memtype()
Date
From: Toshi Kani <toshi.kani@hp.com>

As set_memory_wb() calls free_ram_pages_type(), which then calls
set_page_memtype() with -1, _PGMT_DEFAULT is used for tracking
the WB type. _PGMT_WB is defined but unused. Hence, this patch
renames _PGMT_DEFAULT to _PGMT_WB to clarify the usage, and
releases the slot used by _PGMT_WB before. free_ram_pages_type()
is changed to call set_page_memtype() with _PGMT_WB, and
get_page_memtype() returns _PAGE_CACHE_MODE_WB for _PGMT_WB.

This patch then defines _PGMT_WT to the released slot. This enables
set_page_memtype() to track the WT type.

Signed-off-by: Toshi Kani <toshi.kani@hp.com>
---
arch/x86/mm/pat.c | 60 +++++++++++++++++++++++++++--------------------------
1 file changed, 30 insertions(+), 30 deletions(-)

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 1a2c84c..15d37c3 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -70,18 +70,22 @@ static u64 __read_mostly boot_pat_state;

#ifdef CONFIG_X86_PAT
/*
- * X86 PAT uses page flags WC and Uncached together to keep track of
- * memory type of pages that have backing page struct. X86 PAT supports 3
- * different memory types, _PAGE_CACHE_MODE_WB, _PAGE_CACHE_MODE_WC and
- * _PAGE_CACHE_MODE_UC_MINUS and fourth state where page's memory type has not
- * been changed from its default (value of -1 used to denote this).
- * Note we do not support _PAGE_CACHE_MODE_UC here.
+ * X86 PAT uses page flags arch_1 and uncached together to keep track of
+ * memory type of pages that have backing page struct.
+ *
+ * X86 PAT supports 4 different memory types:
+ * - _PAGE_CACHE_MODE_WB
+ * - _PAGE_CACHE_MODE_WC
+ * - _PAGE_CACHE_MODE_UC_MINUS
+ * - _PAGE_CACHE_MODE_WT
+ *
+ * _PAGE_CACHE_MODE_WB is the default type.
*/

-#define _PGMT_DEFAULT 0
+#define _PGMT_WB 0
#define _PGMT_WC (1UL << PG_arch_1)
#define _PGMT_UC_MINUS (1UL << PG_uncached)
-#define _PGMT_WB (1UL << PG_uncached | 1UL << PG_arch_1)
+#define _PGMT_WT (1UL << PG_uncached | 1UL << PG_arch_1)
#define _PGMT_MASK (1UL << PG_uncached | 1UL << PG_arch_1)
#define _PGMT_CLEAR_MASK (~_PGMT_MASK)

@@ -89,14 +93,14 @@ static inline enum page_cache_mode get_page_memtype(struct page *pg)
{
unsigned long pg_flags = pg->flags & _PGMT_MASK;

- if (pg_flags == _PGMT_DEFAULT)
- return -1;
+ if (pg_flags == _PGMT_WB)
+ return _PAGE_CACHE_MODE_WB;
else if (pg_flags == _PGMT_WC)
return _PAGE_CACHE_MODE_WC;
else if (pg_flags == _PGMT_UC_MINUS)
return _PAGE_CACHE_MODE_UC_MINUS;
else
- return _PAGE_CACHE_MODE_WB;
+ return _PAGE_CACHE_MODE_WT;
}

static inline void set_page_memtype(struct page *pg,
@@ -113,11 +117,12 @@ static inline void set_page_memtype(struct page *pg,
case _PAGE_CACHE_MODE_UC_MINUS:
memtype_flags = _PGMT_UC_MINUS;
break;
- case _PAGE_CACHE_MODE_WB:
- memtype_flags = _PGMT_WB;
+ case _PAGE_CACHE_MODE_WT:
+ memtype_flags = _PGMT_WT;
break;
+ case _PAGE_CACHE_MODE_WB:
default:
- memtype_flags = _PGMT_DEFAULT;
+ memtype_flags = _PGMT_WB;
break;
}

@@ -389,8 +394,11 @@ static int pat_pagerange_is_ram(resource_size_t start, resource_size_t end)

/*
* For RAM pages, we use page flags to mark the pages with appropriate type.
- * The page flags are limited to three types, WB, WC and UC-.
- * WT and WP requests fail with -EINVAL, and UC gets redirected to UC-.
+ * The page flags are limited to four types, WB (default), WC, WT and UC-.
+ * WP request fails with -EINVAL, and UC gets redirected to UC-. Setting
+ * a new memory type is only allowed to a page mapped with the default WB
+ * type.
+ *
* Here we do two pass:
* - Find the memtype of all the pages in the range, look for any conflicts
* - In case of no conflicts, set the new memtype for pages in the range
@@ -402,8 +410,7 @@ static int reserve_ram_pages_type(u64 start, u64 end,
struct page *page;
u64 pfn;

- if ((req_type == _PAGE_CACHE_MODE_WT) ||
- (req_type == _PAGE_CACHE_MODE_WP)) {
+ if (req_type == _PAGE_CACHE_MODE_WP) {
if (new_type)
*new_type = _PAGE_CACHE_MODE_UC_MINUS;
return -EINVAL;
@@ -420,7 +427,7 @@ static int reserve_ram_pages_type(u64 start, u64 end,

page = pfn_to_page(pfn);
type = get_page_memtype(page);
- if (type != -1) {
+ if (type != _PAGE_CACHE_MODE_WB) {
pr_info("x86/PAT: reserve_ram_pages_type failed [mem %#010Lx-%#010Lx], track 0x%x, req 0x%x\n",
start, end - 1, type, req_type);
if (new_type)
@@ -447,7 +454,7 @@ static int free_ram_pages_type(u64 start, u64 end)

for (pfn = (start >> PAGE_SHIFT); pfn < (end >> PAGE_SHIFT); ++pfn) {
page = pfn_to_page(pfn);
- set_page_memtype(page, -1);
+ set_page_memtype(page, _PAGE_CACHE_MODE_WB);
}
return 0;
}
@@ -588,7 +595,7 @@ int free_memtype(u64 start, u64 end)
* Only to be called when PAT is enabled
*
* Returns _PAGE_CACHE_MODE_WB, _PAGE_CACHE_MODE_WC, _PAGE_CACHE_MODE_UC_MINUS
- * or _PAGE_CACHE_MODE_UC
+ * or _PAGE_CACHE_MODE_WT.
*/
static enum page_cache_mode lookup_memtype(u64 paddr)
{
@@ -600,16 +607,9 @@ static enum page_cache_mode lookup_memtype(u64 paddr)

if (pat_pagerange_is_ram(paddr, paddr + PAGE_SIZE)) {
struct page *page;
- page = pfn_to_page(paddr >> PAGE_SHIFT);
- rettype = get_page_memtype(page);
- /*
- * -1 from get_page_memtype() implies RAM page is in its
- * default state and not reserved, and hence of type WB
- */
- if (rettype == -1)
- rettype = _PAGE_CACHE_MODE_WB;

- return rettype;
+ page = pfn_to_page(paddr >> PAGE_SHIFT);
+ return get_page_memtype(page);
}

spin_lock(&memtype_lock);

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