[PATCH] x86/xstate: Rework xsetbv() to use asm goto()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Switch to using a mnemonic, and asm_inline as there's EXTABLE metadata.

Update the types, and adjust parameter names.  The name xfeatures is specific
to xcr0, so rename to val to be more generic, even if there isn't another
writeable xcr yet.

No functional change.

Resolves: https://gitlab.com/xen-project/xen/-/work_items/212
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/xstate.c | 29 +++++++++++++++--------------
 1 file changed, 15 insertions(+), 14 deletions(-)

diff --git a/xen/arch/x86/xstate.c b/xen/arch/x86/xstate.c
index 3d249518a1b7..e8e218caed36 100644
--- a/xen/arch/x86/xstate.c
+++ b/xen/arch/x86/xstate.c
@@ -40,21 +40,22 @@ static DEFINE_PER_CPU(uint64_t, xcr0);
 /* Because XCR0 is cached for each CPU, xsetbv() is not exposed. Users should 
  * use set_xcr0() instead.
  */
-static inline bool xsetbv(u32 index, u64 xfeatures)
+static inline bool xsetbv(uint32_t xcr, uint64_t val)
 {
-    u32 hi = xfeatures >> 32;
-    u32 lo = (u32)xfeatures;
-
-    asm volatile ( "1: .byte 0x0f,0x01,0xd1\n"
-                   "3:                     \n"
-                   ".section .fixup,\"ax\" \n"
-                   "2: xor %0,%0           \n"
-                   "   jmp 3b              \n"
-                   ".previous              \n"
-                   _ASM_EXTABLE(1b, 2b)
-                   : "+a" (lo)
-                   : "c" (index), "d" (hi));
-    return lo != 0;
+    uint32_t hi = val >> 32, lo = val;
+
+    asm_inline goto (
+        "1: xsetbv\n\t"
+        _ASM_EXTABLE(1b, %l[fault])
+        :
+        : "a" (lo), "c" (xcr), "d" (hi)
+        :
+        : fault );
+
+    return true;
+
+ fault:
+    return false;
 }
 
 bool set_xcr0(u64 xfeatures)
-- 
2.39.5