[xen staging-4.19] x86/emul: cope with internal handlers returning X86EMUL_RETRY

[patchbot@xxxxxxx]

commit aabdb184bbf9bef927f1d4786332d3d25e95c7c8
Author:     Roger Pau Monne <roger@xxxxxxxxxxxxxx>
AuthorDate: Fri Aug 7 11:03:48 2026 +0200
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Wed Aug 26 17:50:14 2026 +0100

    x86/emul: cope with internal handlers returning X86EMUL_RETRY
    
    hvm_io_intercept() can return X86EMUL_RETRY, and as such it needs to be
    handled in the switch in hvmemul_do_io() to avoid triggering the BUG() from
    the default case.
    
    Reset the vCPU state to no in-flight IOREQ and return X86EMUL_RETRY so that
    the access is retried.
    
    This is XSA-510 / CVE-2026-79602.
    
    Reported-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
    Signed-off-by: Roger Pau Monné <roger@xxxxxxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    (cherry picked from commit 62aff073266bd83fa2d675913d913134abd3c82b)
---
 xen/arch/x86/hvm/emulate.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index 4dde6a7b4a..a494bf68b1 100644
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -293,6 +293,7 @@ static int hvmemul_do_io(
     switch ( rc )
     {
     case X86EMUL_OKAY:
+    case X86EMUL_RETRY:
         vio->req.state = STATE_IOREQ_NONE;
         break;
     case X86EMUL_UNHANDLEABLE:
--
generated by git-patchbot for /home/xen/git/xen.git#staging-4.19