[PATCH v6 5/5] 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 | 10 +++++-----
 xen/arch/x86/mm.c                    |  8 --------
 3 files changed, 7 insertions(+), 15 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 
60b902060914584957db8afa5c7c1e6abdad4d13..3993d5638626f0948bb7ac8192d2eda187eb1bdb
 100644
--- a/xen/arch/x86/include/asm/processor.h
+++ b/xen/arch/x86/include/asm/processor.h
@@ -94,16 +94,16 @@
 
 /*
  * 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.
+ * MSR_PAT value, and is needed by the Linux i915 driver.
  */
 #define XEN_MSR_PAT ((_AC(X86_MT_WB,  ULL) << 0x00) | \
-                     (_AC(X86_MT_WT,  ULL) << 0x08) | \
+                     (_AC(X86_MT_WC,  ULL) << 0x08) | \
                      (_AC(X86_MT_UCM, ULL) << 0x10) | \
                      (_AC(X86_MT_UC,  ULL) << 0x18) | \
-                     (_AC(X86_MT_WC,  ULL) << 0x20) | \
+                     (_AC(X86_MT_WB,  ULL) << 0x20) | \
                      (_AC(X86_MT_WP,  ULL) << 0x28) | \
-                     (_AC(X86_MT_UC,  ULL) << 0x30) | \
-                     (_AC(X86_MT_UC,  ULL) << 0x38))
+                     (_AC(X86_MT_UCM, ULL) << 0x30) | \
+                     (_AC(X86_MT_WT,  ULL) << 0x38))
 
 #ifndef __ASSEMBLY__
 
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 
bacfb776d688f68dcbf79d83723fff329b75fd18..ea8c69e66c48419031add2e02da0a8eb6af8e49a
 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -6417,14 +6417,6 @@ unsigned long get_upper_mfn_bound(void)
  */
 static void __init __maybe_unused build_assertions(void)
 {
-    /*
-     * If this trips, any guests that blindly rely on the public API in xen.h
-     * (instead of reading the PAT from Xen, as Linux 3.19+ does) will be
-     * broken.  Furthermore, live migration of PV guests between Xen versions
-     * using different PATs will not work.
-     */
-    BUILD_BUG_ON(XEN_MSR_PAT != 0x050100070406ULL);
-
     /*
      * _PAGE_WB must be zero for several reasons, not least because Linux
      * PV guests assume it.
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab