[PATCH v4 07/10] x86: Derive XEN_MSR_PAT from its individual entries

[Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>]

This avoids it being a magic constant that is difficult for humans to
decode.  Use BUILD_BUG_ON to check that the old and new values are
identical.

Signed-off-by: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>
---
 xen/arch/x86/include/asm/processor.h | 9 ++++++++-
 xen/arch/x86/mm.c                    | 9 +++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/include/asm/processor.h 
b/xen/arch/x86/include/asm/processor.h
index 
c3205ed9e10c1a57d23c5ecead66bebd82d87d06..ed71c9c975d56687eb126ec4ca7b271788e5f1d8
 100644
--- a/xen/arch/x86/include/asm/processor.h
+++ b/xen/arch/x86/include/asm/processor.h
@@ -96,7 +96,14 @@
  * 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.
  */
-#define XEN_MSR_PAT _AC(0x050100070406, ULL)
+#define XEN_MSR_PAT ((_AC(X86_MT_WB,  ULL) << 0x00) | \
+                     (_AC(X86_MT_WT,  ULL) << 0x08) | \
+                     (_AC(X86_MT_UCM, ULL) << 0x10) | \
+                     (_AC(X86_MT_UC,  ULL) << 0x18) | \
+                     (_AC(X86_MT_WC,  ULL) << 0x20) | \
+                     (_AC(X86_MT_WP,  ULL) << 0x28) | \
+                     (_AC(X86_MT_UC,  ULL) << 0x30) | \
+                     (_AC(X86_MT_UC,  ULL) << 0x38))
 
 #ifndef __ASSEMBLY__
 
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 
802073a01c5cf4dc3cf1d58d28ea4d4e9e8149c7..eeaa9760d2aa38b5efa2cbf9d99290e7c432ddfe
 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -6357,6 +6357,15 @@ unsigned long get_upper_mfn_bound(void)
     return min(max_mfn, 1UL << (paddr_bits - PAGE_SHIFT)) - 1;
 }
 
+static void __init __maybe_unused build_assertions(void)
+{
+    /*
+     * If this trips, live migration of PV guests to and from this Xen is
+     * broken.
+     */
+    BUILD_BUG_ON(XEN_MSR_PAT != 0x050100070406ULL);
+}
+
 /*
  * Local variables:
  * mode: C
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab