[Xen-devel] [PATCH v2 2/2] x86/xstate: also use alternative asm on xsave side

["Jan Beulich" <JBeulich@xxxxxxxx>]

From: Shuai Ruan <shuai.ruan@xxxxxxxxxxxxxxx>

This patch use alternavtive asm on the xsave side.
As xsaves use modified optimization like xsaveopt, xsaves
may not writing the FPU portion of the save image too.
So xsaves also need some extra tweaks.

Signed-off-by: Shuai Ruan <shuai.ruan@xxxxxxxxxxxxxxx>

Fix XSAVES opcode. Extend the other respective XSAVEOPT conditional to
cover XSAVES as well. Re-wrap comment being adjusted.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/xstate.c
+++ b/xen/arch/x86/xstate.c
@@ -250,27 +250,29 @@ void xsave(struct vcpu *v, uint64_t mask
     uint32_t hmask = mask >> 32;
     uint32_t lmask = mask;
     int word_size = mask & XSTATE_FP ? (cpu_has_fpu_sel ? 8 : 0) : -1;
+#define XSAVE(pfx) \
+        alternative_io_3(".byte " pfx "0x0f,0xae,0x27\n", \
+                         ".byte " pfx "0x0f,0xae,0x37\n", \
+                         X86_FEATURE_XSAVEOPT, \
+                         ".byte " pfx "0x0f,0xc7,0x27\n", \
+                         X86_FEATURE_XSAVEC, \
+                         ".byte " pfx "0x0f,0xc7,0x2f\n", \
+                         X86_FEATURE_XSAVES, \
+                         "=m" (*ptr), \
+                         "a" (lmask), "d" (hmask), "D" (ptr))
 
     if ( word_size <= 0 || !is_pv_32bit_vcpu(v) )
     {
         typeof(ptr->fpu_sse.fip.sel) fcs = ptr->fpu_sse.fip.sel;
         typeof(ptr->fpu_sse.fdp.sel) fds = ptr->fpu_sse.fdp.sel;
 
-        if ( cpu_has_xsaves )
-            asm volatile ( ".byte 0x48,0x0f,0xc7,0x2f"
-                           : "=m" (*ptr)
-                           : "a" (lmask), "d" (hmask), "D" (ptr) );
-        else if ( cpu_has_xsavec )
-            asm volatile ( ".byte 0x48,0x0f,0xc7,0x27"
-                           : "=m" (*ptr)
-                           : "a" (lmask), "d" (hmask), "D" (ptr) );
-        else if ( cpu_has_xsaveopt )
+        if ( cpu_has_xsaveopt || cpu_has_xsaves )
         {
             /*
-             * xsaveopt may not write the FPU portion even when the respective
-             * mask bit is set. For the check further down to work we hence
-             * need to put the save image back into the state that it was in
-             * right after the previous xsaveopt.
+             * XSAVEOPT/XSAVES may not write the FPU portion even when the
+             * respective mask bit is set. For the check further down to work
+             * we hence need to put the save image back into the state that
+             * it was in right after the previous XSAVEOPT.
              */
             if ( word_size > 0 &&
                  (ptr->fpu_sse.x[FPU_WORD_SIZE_OFFSET] == 4 ||
@@ -279,14 +281,9 @@ void xsave(struct vcpu *v, uint64_t mask
                 ptr->fpu_sse.fip.sel = 0;
                 ptr->fpu_sse.fdp.sel = 0;
             }
-            asm volatile ( ".byte 0x48,0x0f,0xae,0x37"
-                           : "=m" (*ptr)
-                           : "a" (lmask), "d" (hmask), "D" (ptr) );
         }
-        else
-            asm volatile ( ".byte 0x48,0x0f,0xae,0x27"
-                           : "=m" (*ptr)
-                           : "a" (lmask), "d" (hmask), "D" (ptr) );
+
+        XSAVE("0x48,");
 
         if ( !(mask & ptr->xsave_hdr.xstate_bv & XSTATE_FP) ||
              /*
@@ -296,7 +293,7 @@ void xsave(struct vcpu *v, uint64_t mask
              (!(ptr->fpu_sse.fsw & 0x0080) &&
               boot_cpu_data.x86_vendor == X86_VENDOR_AMD) )
         {
-            if ( cpu_has_xsaveopt && word_size > 0 )
+            if ( (cpu_has_xsaveopt || cpu_has_xsaves) && word_size > 0 )
             {
                 ptr->fpu_sse.fip.sel = fcs;
                 ptr->fpu_sse.fdp.sel = fds;
@@ -317,24 +314,10 @@ void xsave(struct vcpu *v, uint64_t mask
     }
     else
     {
-        if ( cpu_has_xsaves )
-            asm volatile ( ".byte 0x0f,0xc7,0x2f"
-                           : "=m" (*ptr)
-                           : "a" (lmask), "d" (hmask), "D" (ptr) );
-        else if ( cpu_has_xsavec )
-            asm volatile ( ".byte 0x0f,0xc7,0x27"
-                           : "=m" (*ptr)
-                           : "a" (lmask), "d" (hmask), "D" (ptr) );
-        else if ( cpu_has_xsaveopt )
-            asm volatile ( ".byte 0x0f,0xae,0x37"
-                           : "=m" (*ptr)
-                           : "a" (lmask), "d" (hmask), "D" (ptr) );
-        else
-            asm volatile ( ".byte 0x0f,0xae,0x27"
-                           : "=m" (*ptr)
-                           : "a" (lmask), "d" (hmask), "D" (ptr) );
+        XSAVE("");
         word_size = 4;
     }
+#undef XSAVE
     if ( word_size >= 0 )
         ptr->fpu_sse.x[FPU_WORD_SIZE_OFFSET] = word_size;
 }

Attachment: x86-xsaves-alternative.patch
Description: Text document

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