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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-changelog] [xen master] x86/vm_event: add short-circuit for breakpoints (aka "fast single step")
commit f801b40d20c01eb41bed3157e266a18d34260259
Author: Sergey Kovalev <valor@xxxxxxx>
AuthorDate: Fri Dec 20 16:45:32 2019 +0100
Commit: Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Dec 20 16:45:32 2019 +0100
x86/vm_event: add short-circuit for breakpoints (aka "fast single step")
When using DRAKVUF (or another system using altp2m with shadow pages similar
to what is described in
https://xenproject.org/2016/04/13/stealthy-monitoring-with-xen-altp2m),
after a breakpoint is hit the system switches to the default
unrestricted altp2m view with singlestep enabled. When the singlestep
traps to Xen another vm_event is sent to the monitor agent, which then
normally disables singlestepping and switches the altp2m view back to
the restricted view.
This patch short-circuiting that last part so that it doesn't need to send
the
vm_event out for the singlestep event and should switch back to the
restricted
view in Xen automatically.
This optimization gains about 35% speed-up.
Was tested on Debian branch of Xen 4.12. See at:
https://github.com/skvl/xen/tree/debian/knorrie/4.12/fast-singlestep
Rebased on master:
https://github.com/skvl/xen/tree/fast-singlestep
Signed-off-by: Sergey Kovalev <valor@xxxxxxx>
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
---
xen/arch/x86/hvm/hvm.c | 15 +++++++++++++++
xen/arch/x86/hvm/monitor.c | 9 +++++++++
xen/arch/x86/vm_event.c | 8 ++++++--
xen/include/asm-x86/hvm/hvm.h | 1 +
xen/include/asm-x86/hvm/vcpu.h | 4 ++++
xen/include/public/vm_event.h | 14 ++++++++++++++
6 files changed, 49 insertions(+), 2 deletions(-)
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 3cc6d22dfb..4dfaf35566 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -5099,6 +5099,21 @@ void hvm_toggle_singlestep(struct vcpu *v)
v->arch.hvm.single_step = !v->arch.hvm.single_step;
}
+void hvm_fast_singlestep(struct vcpu *v, uint16_t p2midx)
+{
+ ASSERT(atomic_read(&v->pause_count));
+
+ if ( !hvm_is_singlestep_supported() )
+ return;
+
+ if ( p2midx >= MAX_ALTP2M )
+ return;
+
+ v->arch.hvm.single_step = true;
+ v->arch.hvm.fast_single_step.enabled = true;
+ v->arch.hvm.fast_single_step.p2midx = p2midx;
+}
+
/*
* Segment caches in VMCB/VMCS are inconsistent about which bits are checked,
* important, and preserved across vmentry/exit. Cook the values to make them
diff --git a/xen/arch/x86/hvm/monitor.c b/xen/arch/x86/hvm/monitor.c
index 1f23fe25e8..85996a3edd 100644
--- a/xen/arch/x86/hvm/monitor.c
+++ b/xen/arch/x86/hvm/monitor.c
@@ -28,6 +28,7 @@
#include <asm/hvm/monitor.h>
#include <asm/altp2m.h>
#include <asm/monitor.h>
+#include <asm/p2m.h>
#include <asm/paging.h>
#include <asm/vm_event.h>
#include <public/vm_event.h>
@@ -159,6 +160,14 @@ int hvm_monitor_debug(unsigned long rip, enum
hvm_monitor_debug_type type,
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);
+ curr->arch.hvm.single_step = false;
+ curr->arch.hvm.fast_single_step.enabled = false;
+ curr->arch.hvm.fast_single_step.p2midx = 0;
+ return 0;
+ }
req.reason = VM_EVENT_REASON_SINGLESTEP;
req.u.singlestep.gfn = gfn_of_rip(rip);
sync = true;
diff --git a/xen/arch/x86/vm_event.c b/xen/arch/x86/vm_event.c
index 52c2a71fa0..848d69c1b0 100644
--- a/xen/arch/x86/vm_event.c
+++ b/xen/arch/x86/vm_event.c
@@ -61,7 +61,8 @@ void vm_event_cleanup_domain(struct domain *d)
void vm_event_toggle_singlestep(struct domain *d, struct vcpu *v,
vm_event_response_t *rsp)
{
- if ( !(rsp->flags & VM_EVENT_FLAG_TOGGLE_SINGLESTEP) )
+ if ( !(rsp->flags & (VM_EVENT_FLAG_TOGGLE_SINGLESTEP |
+ VM_EVENT_FLAG_FAST_SINGLESTEP)) )
return;
if ( !is_hvm_domain(d) )
@@ -69,7 +70,10 @@ void vm_event_toggle_singlestep(struct domain *d, struct
vcpu *v,
ASSERT(atomic_read(&v->vm_event_pause_count));
- hvm_toggle_singlestep(v);
+ if ( rsp->flags & VM_EVENT_FLAG_TOGGLE_SINGLESTEP )
+ hvm_toggle_singlestep(v);
+ else
+ hvm_fast_singlestep(v, rsp->u.fast_singlestep.p2midx);
}
void vm_event_register_write_resume(struct vcpu *v, vm_event_response_t *rsp)
diff --git a/xen/include/asm-x86/hvm/hvm.h b/xen/include/asm-x86/hvm/hvm.h
index 1d7b66f927..09793c12e9 100644
--- a/xen/include/asm-x86/hvm/hvm.h
+++ b/xen/include/asm-x86/hvm/hvm.h
@@ -323,6 +323,7 @@ int hvm_debug_op(struct vcpu *v, int32_t op);
/* Caller should pause vcpu before calling this function */
void hvm_toggle_singlestep(struct vcpu *v);
+void hvm_fast_singlestep(struct vcpu *v, uint16_t p2midx);
int hvm_hap_nested_page_fault(paddr_t gpa, unsigned long gla,
struct npfec npfec);
diff --git a/xen/include/asm-x86/hvm/vcpu.h b/xen/include/asm-x86/hvm/vcpu.h
index 38f5c2bb9b..8b84941111 100644
--- a/xen/include/asm-x86/hvm/vcpu.h
+++ b/xen/include/asm-x86/hvm/vcpu.h
@@ -172,6 +172,10 @@ struct hvm_vcpu {
bool flag_dr_dirty;
bool debug_state_latch;
bool single_step;
+ struct {
+ bool enabled;
+ uint16_t p2midx;
+ } fast_single_step;
struct hvm_vcpu_asid n1asid;
diff --git a/xen/include/public/vm_event.h b/xen/include/public/vm_event.h
index aa54c86325..0ffec27d62 100644
--- a/xen/include/public/vm_event.h
+++ b/xen/include/public/vm_event.h
@@ -110,6 +110,15 @@
* interrupt pending after resuming the VCPU.
*/
#define VM_EVENT_FLAG_GET_NEXT_INTERRUPT (1 << 10)
+/*
+ * Execute fast singlestepping on vm_event response.
+ * Requires the vCPU to be paused already (synchronous events only).
+ *
+ * On a response requires setting the p2midx field of fast_singlestep to which
+ * Xen will switch the vCPU to on the occurance of the first singlestep, after
+ * which singlestep gets automatically disabled.
+ */
+#define VM_EVENT_FLAG_FAST_SINGLESTEP (1 << 11)
/*
* Reasons for the vm event request
@@ -276,6 +285,10 @@ struct vm_event_singlestep {
uint64_t gfn;
};
+struct vm_event_fast_singlestep {
+ uint16_t p2midx;
+};
+
struct vm_event_debug {
uint64_t gfn;
uint32_t insn_length;
@@ -363,6 +376,7 @@ typedef struct vm_event_st {
struct vm_event_mov_to_msr mov_to_msr;
struct vm_event_desc_access desc_access;
struct vm_event_singlestep singlestep;
+ struct vm_event_fast_singlestep fast_singlestep;
struct vm_event_debug software_breakpoint;
struct vm_event_debug debug_exception;
struct vm_event_cpuid cpuid;
--
generated by git-patchbot for /home/xen/git/xen.git#master
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