[RFC PATCH 1/11] x86, mm, pat: Redefine _PAGE_CACHE_UC as UC_MINUS

From: Toshi Kani
Date: Tue Jul 15 2014 - 15:45:39 EST

ioremap_nocache() and other interfaces that set the uncached memory
type use _PAGE_CACHE_UC_MINUS in order to support legacy graphics
drivers using MTRRs to overwrite it to WC. _PAGE_CACHE_UC is defined,
but is unused on the systems with the PAT feature.

This patch redefines _PAGE_CACHE_UC to _PAGE_CACHE_UC_MINUS, and
and frees up the PA3/7 slot in the PAT MSR that was used for
_PAGE_CACHE_UC. This keeps _PAGE_CACHE_UC defined in case out-of-tree
drivers refer it.

Note: The legacy code in phys_mem_access_prot_allowed() that sets
_PAGE_CACHE_UC for Pentiums and earlier processors is changed to
set the PCD & PWT bits in order to avoid any change. They do not
support PAT and MTRRs.

Signed-off-by: Toshi Kani <toshi.kani@xxxxxx>
---
arch/x86/include/asm/pgtable_types.h | 10 +++++-----
arch/x86/mm/ioremap.c | 14 +++++---------
arch/x86/mm/pat.c | 9 +--------
arch/x86/mm/pat_internal.h | 1 -
4 files changed, 11 insertions(+), 23 deletions(-)

diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index f216963..03d40da 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -133,7 +133,7 @@
#define _PAGE_CACHE_WB (0)
#define _PAGE_CACHE_WC (_PAGE_PWT)
#define _PAGE_CACHE_UC_MINUS (_PAGE_PCD)
-#define _PAGE_CACHE_UC (_PAGE_PCD | _PAGE_PWT)
+#define _PAGE_CACHE_UC (_PAGE_CACHE_UC_MINUS)

#define PAGE_NONE __pgprot(_PAGE_PROTNONE | _PAGE_ACCESSED)
#define PAGE_SHARED __pgprot(_PAGE_PRESENT | _PAGE_RW | _PAGE_USER | \
@@ -157,13 +157,13 @@

#define __PAGE_KERNEL_RO (__PAGE_KERNEL & ~_PAGE_RW)
#define __PAGE_KERNEL_RX (__PAGE_KERNEL_EXEC & ~_PAGE_RW)
-#define __PAGE_KERNEL_EXEC_NOCACHE (__PAGE_KERNEL_EXEC | _PAGE_PCD | _PAGE_PWT)
+#define __PAGE_KERNEL_EXEC_NOCACHE (__PAGE_KERNEL_EXEC | _PAGE_CACHE_UC)
#define __PAGE_KERNEL_WC (__PAGE_KERNEL | _PAGE_CACHE_WC)
-#define __PAGE_KERNEL_NOCACHE (__PAGE_KERNEL | _PAGE_PCD | _PAGE_PWT)
-#define __PAGE_KERNEL_UC_MINUS (__PAGE_KERNEL | _PAGE_PCD)
+#define __PAGE_KERNEL_NOCACHE (__PAGE_KERNEL | _PAGE_CACHE_UC)
+#define __PAGE_KERNEL_UC_MINUS (__PAGE_KERNEL | _PAGE_CACHE_UC_MINUS)
#define __PAGE_KERNEL_VSYSCALL (__PAGE_KERNEL_RX | _PAGE_USER)
#define __PAGE_KERNEL_VVAR (__PAGE_KERNEL_RO | _PAGE_USER)
-#define __PAGE_KERNEL_VVAR_NOCACHE (__PAGE_KERNEL_VVAR | _PAGE_PCD | _PAGE_PWT)
+#define __PAGE_KERNEL_VVAR_NOCACHE (__PAGE_KERNEL_VVAR | _PAGE_CACHE_UC)
#define __PAGE_KERNEL_LARGE (__PAGE_KERNEL | _PAGE_PSE)
#define __PAGE_KERNEL_LARGE_NOCACHE (__PAGE_KERNEL | _PAGE_CACHE_UC | _PAGE_PSE)
#define __PAGE_KERNEL_LARGE_EXEC (__PAGE_KERNEL_EXEC | _PAGE_PSE)
diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index baff1da..282829f 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -35,7 +35,7 @@ int ioremap_change_attr(unsigned long vaddr, unsigned long size,
int err;

switch (prot_val) {
- case _PAGE_CACHE_UC:
+ case _PAGE_CACHE_UC_MINUS:
default:
err = _set_memory_uc(vaddr, nrpages);
break;
@@ -142,11 +142,8 @@ static void __iomem *__ioremap_caller(resource_size_t phys_addr,
}

switch (prot_val) {
- case _PAGE_CACHE_UC:
- default:
- prot = PAGE_KERNEL_IO_NOCACHE;
- break;
case _PAGE_CACHE_UC_MINUS:
+ default:
prot = PAGE_KERNEL_IO_UC_MINUS;
break;
case _PAGE_CACHE_WC:
@@ -218,11 +215,10 @@ void __iomem *ioremap_nocache(resource_size_t phys_addr, unsigned long size)
* pat_enabled ? _PAGE_CACHE_UC : _PAGE_CACHE_UC_MINUS;
*
* Till we fix all X drivers to use ioremap_wc(), we will use
- * UC MINUS.
+ * UC MINUS. _PAGE_CACHE_UC is also defined as _PAGE_CACHE_UC_MINUS
+ * in pgtable_types.h.
*/
- unsigned long val = _PAGE_CACHE_UC_MINUS;
-
- return __ioremap_caller(phys_addr, size, val,
+ return __ioremap_caller(phys_addr, size, _PAGE_CACHE_UC_MINUS,
__builtin_return_address(0));
}
EXPORT_SYMBOL(ioremap_nocache);
diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 6574388..c3567a5 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -213,12 +213,6 @@ static int reserve_ram_pages_type(u64 start, u64 end, unsigned long req_type,
struct page *page;
u64 pfn;

- if (req_type == _PAGE_CACHE_UC) {
- /* We do not support strong UC */
- WARN_ON_ONCE(1);
- req_type = _PAGE_CACHE_UC_MINUS;
- }
-
for (pfn = (start >> PAGE_SHIFT); pfn < (end >> PAGE_SHIFT); ++pfn) {
unsigned long type;

@@ -261,7 +255,6 @@ static int free_ram_pages_type(u64 start, u64 end)
* - _PAGE_CACHE_WB
* - _PAGE_CACHE_WC
* - _PAGE_CACHE_UC_MINUS
- * - _PAGE_CACHE_UC
*
* If new_type is NULL, function will return an error if it cannot reserve the
* region with req_type. If new_type is non-NULL, function will return
@@ -543,7 +536,7 @@ int phys_mem_access_prot_allowed(struct file *file, unsigned long pfn,
boot_cpu_has(X86_FEATURE_CYRIX_ARR) ||
boot_cpu_has(X86_FEATURE_CENTAUR_MCR)) &&
(pfn << PAGE_SHIFT) >= __pa(high_memory)) {
- flags = _PAGE_CACHE_UC;
+ flags = _PAGE_PCD | _PAGE_PWT; /* UC w/o PAT */
}
#endif

diff --git a/arch/x86/mm/pat_internal.h b/arch/x86/mm/pat_internal.h
index 77e5ba1..2593d40 100644
--- a/arch/x86/mm/pat_internal.h
+++ b/arch/x86/mm/pat_internal.h
@@ -17,7 +17,6 @@ struct memtype {
static inline 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";
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