[Xen-changelog] [xen stable-4.9] xpti: fix bug in double fault handling

[patchbot@xxxxxxx]

commit f7889b33a9125c4b64fad6d049724c985d79b9d0
Author:     Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Fri May 18 11:57:06 2018 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri May 18 11:57:06 2018 +0200

    xpti: fix bug in double fault handling
    
    When entering the hypervisor via the double fault handler resetting
    xen_cr3 was missing. This led to switching to pv_cr3 when returning
    from the next following exception, so repair this in order to allow
    exception handling to work even after a double fault.
    
    Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Tested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: d80af845de7a4db01a4a3b4d779e0e0dcb5e738b
    master date: 2018-04-23 16:13:01 +0200
---
 xen/arch/x86/x86_64/entry.S | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S
index 964f3121b9..7004f521ce 100644
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -789,12 +789,14 @@ ENTRY(double_fault)
         /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */
 
         mov   STACK_CPUINFO_FIELD(xen_cr3)(%r14), %rbx
-        test  %rbx, %rbx
+        neg   %rbx
         jz    .Ldblf_cr3_okay
         jns   .Ldblf_cr3_load
+        mov   %rbx, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
         neg   %rbx
 .Ldblf_cr3_load:
         mov   %rbx, %cr3
+        movq $0, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
 .Ldblf_cr3_okay:
 
         movq  %rsp,%rdi
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.9

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