[xen staging] x86/pv: Adjust the save_segments() comment regarding MSR_GS_SHADOW

[patchbot@xxxxxxx]

commit a41bba43a7f913b1e952a8693af825ad315ee2d1
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Thu Apr 9 10:07:32 2026 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Jul 7 17:19:38 2026 +0100

    x86/pv: Adjust the save_segments() comment regarding MSR_GS_SHADOW
    
    This is slightly stale mentioning SWAPGS and not LKGS.  However, take the
    opportunity to make the comment more general and less likely to bitrot.
    
    It would be a serious vulnerability for operating systems generally if CPL3
    could modify GS_SHADOW at all.
    
    No functional change.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Teddy Astie <teddy.astie@xxxxxxxxxx>
---
 xen/arch/x86/domain.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 1d458f1372..4252339978 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1951,9 +1951,8 @@ static void load_segments(struct vcpu *n)
  * changes to bases can also be made with the WR{FS,GS}BASE instructions, when
  * enabled.
  *
- * Guests however cannot use SWAPGS, so there is no mechanism to modify the
- * inactive GS base behind Xen's back.  Therefore, Xen's copy of the inactive
- * GS base is still accurate, and doesn't need reading back from hardware.
+ * Guests cannot modify the inactive GS base behind Xen's back.  Therefore
+ * Xen's copy is still accurate and doesn't need reading back.
  *
  * Under FRED, hardware automatically swaps GS for us, so SHADOW_GS is the
  * active GS from the guest's point of view.
--
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