[xen master] x86/entry: Partially revert IST-exit checks

[patchbot@xxxxxxx]

commit 9b57c800b79b96769ea3dcd6468578fa664d19f9
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue Sep 19 11:23:34 2023 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Sep 19 19:35:22 2023 +0100

    x86/entry: Partially revert IST-exit checks
    
    The patch adding check_ist_exit() didn't account for the fact that
    reset_stack_and_jump() is not an ABI-preserving boundary.  The IST-ness in
    %r12 doesn't survive into the next context, and is a stale value C.
    
    This shows up in Gitlab CI for the Clang build:
    
      https://gitlab.com/xen-project/people/andyhhp/xen/-/jobs/5112783827
    
    and in OSSTest for GCC 8:
    
      
http://logs.test-lab.xenproject.org/osstest/logs/183045/test-amd64-amd64-xl-qemuu-debianhvm-amd64/serial-pinot0.log
    
    There's no straightforward way to reconstruct the IST-exit-ness on the
    exit-to-guest path after a context switch.  For now, we only need IST-exit 
on
    the return-to-Xen path.
    
    Fixes: 21bdc25b05a0 ("x86/entry: Track the IST-ness of an entry for the 
exit paths")
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/x86_64/compat/entry.S | 9 +--------
 xen/arch/x86/x86_64/entry.S        | 9 +--------
 2 files changed, 2 insertions(+), 16 deletions(-)

diff --git a/xen/arch/x86/x86_64/compat/entry.S 
b/xen/arch/x86/x86_64/compat/entry.S
index 7504bfb4f3..bd5abd8040 100644
--- a/xen/arch/x86/x86_64/compat/entry.S
+++ b/xen/arch/x86/x86_64/compat/entry.S
@@ -117,15 +117,8 @@ compat_process_trap:
         call  compat_create_bounce_frame
         jmp   compat_test_all_events
 
-/* %rbx: struct vcpu, %r12: ist_exit, interrupts disabled */
+/* %rbx: struct vcpu, interrupts disabled */
 ENTRY(compat_restore_all_guest)
-
-#ifdef CONFIG_DEBUG
-        mov   %rsp, %rdi
-        mov   %r12, %rsi
-        call  check_ist_exit
-#endif
-
         ASSERT_INTERRUPTS_DISABLED
         mov   $~(X86_EFLAGS_IOPL | X86_EFLAGS_VM), %r11d
         and   UREGS_eflags(%rsp),%r11d
diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S
index 988ef6cbc6..5ca74f5f62 100644
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -142,15 +142,8 @@ process_trap:
 
         .section .text.entry, "ax", @progbits
 
-/* %rbx: struct vcpu, %r12: ist_exit, interrupts disabled */
+/* %rbx: struct vcpu, interrupts disabled */
 restore_all_guest:
-
-#ifdef CONFIG_DEBUG
-        mov   %rsp, %rdi
-        mov   %r12, %rsi
-        call  check_ist_exit
-#endif
-
         ASSERT_INTERRUPTS_DISABLED
 
         /* Stash guest SPEC_CTRL value while we can read struct vcpu. */
--
generated by git-patchbot for /home/xen/git/xen.git#master