[Xen-changelog] [xen stable-4.3] x86: refine FPU selector handling code for XSAVEOPT

[patchbot@xxxxxxx]

commit 014f835efaf9caa9a112b7f7a7ffad6dd682c77d
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Wed Aug 7 16:55:05 2013 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Aug 7 16:55:05 2013 +0200

    x86: refine FPU selector handling code for XSAVEOPT
    
    Some extra tweaks are necessary to deal with the situation of XSAVEOPT
    not writing the FPU portion of the save image (due to it detecting that
    the register state did not get modified since the last XRSTOR).
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Tested-by: Ben Guthro <ben.guthro@xxxxxxxxx>
    Acked-by: Keir Fraser <keir@xxxxxxx>
    master commit: c58d9f2f4844c2ce8859a8d0f26a54cd058eb51f
    master date: 2013-08-05 18:42:37 +0200
---
 xen/arch/x86/xstate.c |   25 +++++++++++++++++++++++++
 1 files changed, 25 insertions(+), 0 deletions(-)

diff --git a/xen/arch/x86/xstate.c b/xen/arch/x86/xstate.c
index d52dbd7..ce94d28 100644
--- a/xen/arch/x86/xstate.c
+++ b/xen/arch/x86/xstate.c
@@ -71,10 +71,28 @@ void xsave(struct vcpu *v, uint64_t mask)
 
     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_xsaveopt )
+        {
+            /*
+             * 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.
+             */
+            if ( word_size > 0 &&
+                 (ptr->fpu_sse.x[FPU_WORD_SIZE_OFFSET] == 4 ||
+                  ptr->fpu_sse.x[FPU_WORD_SIZE_OFFSET] == 2) )
+            {
+                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)
@@ -87,7 +105,14 @@ 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 )
+            {
+                ptr->fpu_sse.fip.sel = fcs;
+                ptr->fpu_sse.fdp.sel = fds;
+            }
             return;
+        }
 
         if ( word_size > 0 &&
              !((ptr->fpu_sse.fip.addr | ptr->fpu_sse.fdp.addr) >> 32) )
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.3

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