[PATCH v2 14/14] x86: Use Linux's PAT

[Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>]

This is purely for testing, to see if it works around a bug in i915.  It
is not intended to be merged.

NOT-signed-off-by: DO NOT MERGE
---
 xen/arch/x86/include/asm/page.h      |  4 ++--
 xen/arch/x86/include/asm/processor.h | 13 +++++--------
 xen/arch/x86/mm.c                    |  2 --
 3 files changed, 7 insertions(+), 12 deletions(-)

diff --git a/xen/arch/x86/include/asm/page.h b/xen/arch/x86/include/asm/page.h
index 
b585235d064a567082582c8e92a4e8283fd949ca..ab9b46f1d0901e50a83fd035ff28d1bda0b781a2
 100644
--- a/xen/arch/x86/include/asm/page.h
+++ b/xen/arch/x86/include/asm/page.h
@@ -333,11 +333,11 @@ void efi_update_l4_pgtable(unsigned int l4idx, 
l4_pgentry_t);
 
 /* Memory types, encoded under Xen's choice of MSR_PAT. */
 #define _PAGE_WB         (                                0)
-#define _PAGE_WT         (                        _PAGE_PWT)
+#define _PAGE_WC         (                        _PAGE_PWT)
 #define _PAGE_UCM        (            _PAGE_PCD            )
 #define _PAGE_UC         (            _PAGE_PCD | _PAGE_PWT)
-#define _PAGE_WC         (_PAGE_PAT                        )
 #define _PAGE_WP         (_PAGE_PAT |             _PAGE_PWT)
+#define _PAGE_WT         (_PAGE_PAT | _PAGE_PCD | _PAGE_PWT)
 
 /*
  * Debug option: Ensure that granted mappings are not implicitly unmapped.
diff --git a/xen/arch/x86/include/asm/processor.h 
b/xen/arch/x86/include/asm/processor.h
index 
9535b1f7f49d75e6853365e6109a33359c740f4f..04e9674ea76ce11a2ac00fb7457f3ce97db24d70
 100644
--- a/xen/arch/x86/include/asm/processor.h
+++ b/xen/arch/x86/include/asm/processor.h
@@ -92,18 +92,15 @@
                           X86_EFLAGS_NT|X86_EFLAGS_DF|X86_EFLAGS_IF|    \
                           X86_EFLAGS_TF)
 
-/*
- * Host IA32_CR_PAT value to cover all memory types.  This is not the default
- * MSR_PAT value, and is an ABI with PV guests.
- */
+/* Linux PAT, required by i915 driver */
 #define XEN_MSR_PAT (X86_MT_WB  << 0x00 | \
-                     X86_MT_WT  << 0x08 | \
+                     X86_MT_WC  << 0x08 | \
                      X86_MT_UCM << 0x10 | \
                      X86_MT_UC  << 0x18 | \
-                     X86_MT_WC  << 0x20 | \
+                     X86_MT_WB  << 0x20 | \
                      X86_MT_WP  << 0x28 | \
-                     X86_MT_UC  << 0x30 | \
-                     X86_MT_UC  << 0x38 | \
+                     X86_MT_UCM << 0x30 | \
+                     X86_MT_WT  << 0x38 | \
                      0)
 
 #ifndef __ASSEMBLY__
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 
a199bb05031e0fb1ea4c25ef1d641afe71690d74..b844ff441d8ddd371bc69f4e43c796d03638cbb3
 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -6382,8 +6382,6 @@ static void __init __maybe_unused build_assertions(void)
 {
     /* A bunch of static assertions to check that the XEN_MSR_PAT is valid
      * and consistent with the _PAGE_* macros */
-    BUILD_BUG_ON(XEN_MSR_PAT != 0x050100070406ULL &&
-                 "wrong XEN_MSR_PAT breaks PV guests");
     BUILD_BUG_ON(_PAGE_WB && "Linux requires _PAGE_WB to be 0");
 #define PAT_VALUE(v) (0xFF & (XEN_MSR_PAT >> (8 * (v))))
 #define BAD_VALUE(v) ((v) < 0 || (v) > 7 ||                                    
\
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab