x86/monitor: allow fast-singlestepping without enabling singlestep monitor

Commit Message

Petr Beneš April 14, 2024, 6:21 p.m. UTC

From: Petr Beneš <[e-mail]>

Reorder the condition checks within the HVM_MONITOR_SINGLESTEP_BREAKPOINT
case to enable fast singlestepping independently of the singlestep monitor
being enabled. Previously, fast singlestepping required the singlestep
monitor to be explicitly enabled through xc_monitor_singlestep, even though
it operates entirely within Xen and does not generate external events.

Signed-off-by: Petr Beneš <[e-mail]>
---
 xen/arch/x86/hvm/monitor.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Tamas K Lengyel April 23, 2024, 9:42 p.m. UTC | #1

On Sun, Apr 14, 2024 at 2:21 PM Petr Beneš <[e-mail]> wrote:
>
> From: Petr Beneš <[e-mail]>
>
> Reorder the condition checks within the HVM_MONITOR_SINGLESTEP_BREAKPOINT
> case to enable fast singlestepping independently of the singlestep monitor
> being enabled. Previously, fast singlestepping required the singlestep
> monitor to be explicitly enabled through xc_monitor_singlestep, even though
> it operates entirely within Xen and does not generate external events.
>
> Signed-off-by: Petr Beneš <[e-mail]>

Acked-by: Tamas K Lengyel <[e-mail]>

Patch

diff --git a/xen/arch/x86/hvm/monitor.c b/xen/arch/x86/hvm/monitor.c
index 4f500beaf5..2a8ff07ec9 100644
--- a/xen/arch/x86/hvm/monitor.c
+++ b/xen/arch/x86/hvm/monitor.c
@@ -178,8 +178,6 @@  int hvm_monitor_debug(unsigned long rip, enum hvm_monitor_debug_type type,
         break;
 
     case HVM_MONITOR_SINGLESTEP_BREAKPOINT:
-        if ( !ad->monitor.singlestep_enabled )
-            return 0;
         if ( curr->arch.hvm.fast_single_step.enabled )
         {
             p2m_altp2m_check(curr, curr->arch.hvm.fast_single_step.p2midx);
@@ -188,6 +186,8 @@  int hvm_monitor_debug(unsigned long rip, enum hvm_monitor_debug_type type,
             curr->arch.hvm.fast_single_step.p2midx = 0;
             return 0;
         }
+        if ( !ad->monitor.singlestep_enabled )
+            return 0;
         req.reason = VM_EVENT_REASON_SINGLESTEP;
         req.u.singlestep.gfn = gfn_of_rip(rip);
         sync = true;