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[XEN][PATCH] xen: make VMTRACE support optional


  • To: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Grygorii Strashko <grygorii_strashko@xxxxxxxx>
  • Date: Fri, 31 Oct 2025 21:20:06 +0000
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  • Cc: Grygorii Strashko <grygorii_strashko@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Tamas K Lengyel <tamas@xxxxxxxxxxxxx>, Alexandru Isaila <aisaila@xxxxxxxxxxxxxxx>, Petre Pircalabu <ppircalabu@xxxxxxxxxxxxxxx>, Penny Zheng <Penny.Zheng@xxxxxxx>
  • Delivery-date: Fri, 31 Oct 2025 21:20:34 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Thread-index: AQHcSqwhtyHzg01iHka3JeM7CuPAbQ==
  • Thread-topic: [XEN][PATCH] xen: make VMTRACE support optional

From: Grygorii Strashko <grygorii_strashko@xxxxxxxx>

The VMTRACE feature depends on Platform/Arch HW and code support and now
can be used only on x86 HVM with Intel VT-x (INTEL_VMX) enabled.
This makes VMTRACE support optional by introducing two Kconfig options:
- CONFIG_HAS_VMTRACE which allows Platform/Arch to advertise VMTRACE
support readiness
- CONFIG_VMTRACE to enable/disable the feature.

Signed-off-by: Grygorii Strashko <grygorii_strashko@xxxxxxxx>
---
Based on top of patch "domain: adjust soft-reset arch dependency" [1]

[1] 
https://patchwork.kernel.org/project/xen-devel/patch/c9c8c9c6-a155-4986-bf77-5766cdcd6024@xxxxxxxx/

 xen/Kconfig.debug                       | 15 +++++++++++++++
 xen/arch/x86/domctl.c                   |  4 ++++
 xen/arch/x86/hvm/Kconfig                |  1 +
 xen/arch/x86/hvm/vmx/vmcs.c             |  2 ++
 xen/arch/x86/hvm/vmx/vmx.c              | 10 ++++++++++
 xen/arch/x86/include/asm/guest-msr.h    |  2 ++
 xen/arch/x86/include/asm/hvm/hvm.h      |  9 +++++++++
 xen/arch/x86/include/asm/hvm/vmx/vmcs.h |  2 ++
 xen/arch/x86/mm/mem_sharing.c           |  2 ++
 xen/arch/x86/vm_event.c                 |  6 ++++--
 xen/common/domain.c                     | 10 ++++++++++
 xen/common/memory.c                     |  6 ++++++
 xen/common/vm_event.c                   |  3 ++-
 xen/include/xen/domain.h                |  4 ++++
 xen/include/xen/sched.h                 |  4 ++++
 15 files changed, 77 insertions(+), 3 deletions(-)

diff --git a/xen/Kconfig.debug b/xen/Kconfig.debug
index d900d926c555..70ec4f0d14a5 100644
--- a/xen/Kconfig.debug
+++ b/xen/Kconfig.debug
@@ -155,4 +155,19 @@ config DEBUG_INFO
          "make install-xen" for installing xen.efi, stripping needs to be
          done outside the Xen build environment).
 
+config HAS_VMTRACE
+    bool
+
+config VMTRACE
+    bool "HW VM tracing support"
+    depends on HAS_VMTRACE
+    default y
+    help
+      Enables HW VM tracing support which allows to configure HW processor
+      features (vmtrace_op) to enable capturing information about software
+      execution using dedicated hardware facilities with minimal interference
+      to the software being traced. The trace date can be retrieved using 
buffer
+      shared between Xen and domain
+      (see XENMEM_acquire_resource(XENMEM_resource_vmtrace_buf)).
+
 endmenu
diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
index 6153e3c07e2d..d9521808dcba 100644
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -154,6 +154,7 @@ void arch_get_domain_info(const struct domain *d,
 static int do_vmtrace_op(struct domain *d, struct xen_domctl_vmtrace_op *op,
                          XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
 {
+#ifdef CONFIG_VMTRACE
     struct vcpu *v;
     int rc;
 
@@ -198,6 +199,9 @@ static int do_vmtrace_op(struct domain *d, struct 
xen_domctl_vmtrace_op *op,
     vcpu_unpause(v);
 
     return rc;
+#else
+    return -EOPNOTSUPP;
+#endif
 }
 
 #define MAX_IOPORTS 0x10000
diff --git a/xen/arch/x86/hvm/Kconfig b/xen/arch/x86/hvm/Kconfig
index c1a131d1851a..c017a77fffe0 100644
--- a/xen/arch/x86/hvm/Kconfig
+++ b/xen/arch/x86/hvm/Kconfig
@@ -29,6 +29,7 @@ config INTEL_VMX
        bool "Intel VT-x" if EXPERT
        default INTEL
        select ARCH_VCPU_IOREQ_COMPLETION
+       select HAS_VMTRACE
        help
          Enables virtual machine extensions on platforms that implement the
          Intel Virtualization Technology (Intel VT-x).
diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
index ab8b1c87ec0f..3728a9140223 100644
--- a/xen/arch/x86/hvm/vmx/vmcs.c
+++ b/xen/arch/x86/hvm/vmx/vmcs.c
@@ -300,6 +300,7 @@ static int vmx_init_vmcs_config(bool bsp)
     rdmsrl(MSR_IA32_VMX_MISC, _vmx_misc_cap);
 
     /* Check whether IPT is supported in VMX operation. */
+#ifdef CONFIG_VMTRACE
     if ( bsp )
         vmtrace_available = cpu_has_proc_trace &&
                             (_vmx_misc_cap & VMX_MISC_PROC_TRACE);
@@ -310,6 +311,7 @@ static int vmx_init_vmcs_config(bool bsp)
                smp_processor_id());
         return -EINVAL;
     }
+#endif
 
     if ( caps.cpu_based_exec_control & CPU_BASED_ACTIVATE_SECONDARY_CONTROLS )
     {
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index b65981077295..f1588cd90b2d 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -622,6 +622,7 @@ static void cf_check domain_creation_finished(struct domain 
*d)
 
 static void vmx_init_ipt(struct vcpu *v)
 {
+#ifdef CONFIG_VMTRACE
     unsigned int size = v->domain->vmtrace_size;
 
     if ( !size )
@@ -632,6 +633,7 @@ static void vmx_init_ipt(struct vcpu *v)
     ASSERT(size >= PAGE_SIZE && (size & (size - 1)) == 0);
 
     v->arch.msrs->rtit.output_limit = size - 1;
+#endif
 }
 
 static int cf_check vmx_vcpu_initialise(struct vcpu *v)
@@ -724,11 +726,13 @@ static void vmx_save_guest_msrs(struct vcpu *v)
      */
     v->arch.hvm.vmx.shadow_gs = read_gs_shadow();
 
+#ifdef CONFIG_VMTRACE
     if ( v->arch.hvm.vmx.ipt_active )
     {
         rdmsrl(MSR_RTIT_OUTPUT_MASK, msrs->rtit.output_mask);
         rdmsrl(MSR_RTIT_STATUS, msrs->rtit.status);
     }
+#endif
 
     if ( cp->feat.pks )
         msrs->pkrs = rdpkrs_and_cache();
@@ -747,12 +751,14 @@ static void vmx_restore_guest_msrs(struct vcpu *v)
     if ( cpu_has_msr_tsc_aux )
         wrmsr_tsc_aux(msrs->tsc_aux);
 
+#ifdef CONFIG_VMTRACE
     if ( v->arch.hvm.vmx.ipt_active )
     {
         wrmsrl(MSR_RTIT_OUTPUT_BASE, page_to_maddr(v->vmtrace.pg));
         wrmsrl(MSR_RTIT_OUTPUT_MASK, msrs->rtit.output_mask);
         wrmsrl(MSR_RTIT_STATUS, msrs->rtit.status);
     }
+#endif
 
     if ( cp->feat.pks )
         wrpkrs(msrs->pkrs);
@@ -2626,6 +2632,7 @@ static bool cf_check vmx_get_pending_event(
     return true;
 }
 
+#ifdef CONFIG_VMTRACE
 /*
  * We only let vmtrace agents see and modify a subset of bits in MSR_RTIT_CTL.
  * These all pertain to data-emitted into the trace buffer(s).  Must not
@@ -2768,6 +2775,7 @@ static int cf_check vmtrace_reset(struct vcpu *v)
     v->arch.msrs->rtit.status = 0;
     return 0;
 }
+#endif
 
 static uint64_t cf_check vmx_get_reg(struct vcpu *v, unsigned int reg)
 {
@@ -2940,11 +2948,13 @@ static struct hvm_function_table __initdata_cf_clobber 
vmx_function_table = {
     .altp2m_vcpu_emulate_ve = vmx_vcpu_emulate_ve,
     .altp2m_vcpu_emulate_vmfunc = vmx_vcpu_emulate_vmfunc,
 #endif
+#ifdef CONFIG_VMTRACE
     .vmtrace_control = vmtrace_control,
     .vmtrace_output_position = vmtrace_output_position,
     .vmtrace_set_option = vmtrace_set_option,
     .vmtrace_get_option = vmtrace_get_option,
     .vmtrace_reset = vmtrace_reset,
+#endif
 
     .get_reg = vmx_get_reg,
     .set_reg = vmx_set_reg,
diff --git a/xen/arch/x86/include/asm/guest-msr.h 
b/xen/arch/x86/include/asm/guest-msr.h
index 5f0cb0a93995..702f47fe1e16 100644
--- a/xen/arch/x86/include/asm/guest-msr.h
+++ b/xen/arch/x86/include/asm/guest-msr.h
@@ -50,6 +50,7 @@ struct vcpu_msrs
         };
     } misc_features_enables;
 
+#ifdef CONFIG_VMTRACE
     /*
      * 0x00000560 ... 57x - MSR_RTIT_*
      *
@@ -81,6 +82,7 @@ struct vcpu_msrs
             };
         };
     } rtit;
+#endif
 
     /*
      * 0x000006e1 - MSR_PKRS - Protection Key Supervisor.
diff --git a/xen/arch/x86/include/asm/hvm/hvm.h 
b/xen/arch/x86/include/asm/hvm/hvm.h
index 7412256a2dab..728b9624522f 100644
--- a/xen/arch/x86/include/asm/hvm/hvm.h
+++ b/xen/arch/x86/include/asm/hvm/hvm.h
@@ -234,12 +234,14 @@ struct hvm_function_table {
     int (*altp2m_vcpu_emulate_vmfunc)(const struct cpu_user_regs *regs);
 #endif
 
+#ifdef CONFIG_VMTRACE
     /* vmtrace */
     int (*vmtrace_control)(struct vcpu *v, bool enable, bool reset);
     int (*vmtrace_output_position)(struct vcpu *v, uint64_t *pos);
     int (*vmtrace_set_option)(struct vcpu *v, uint64_t key, uint64_t value);
     int (*vmtrace_get_option)(struct vcpu *v, uint64_t key, uint64_t *value);
     int (*vmtrace_reset)(struct vcpu *v);
+#endif
 
     uint64_t (*get_reg)(struct vcpu *v, unsigned int reg);
     void (*set_reg)(struct vcpu *v, unsigned int reg, uint64_t val);
@@ -738,6 +740,7 @@ static inline bool altp2m_vcpu_emulate_ve(struct vcpu *v)
 bool altp2m_vcpu_emulate_ve(struct vcpu *v);
 #endif /* CONFIG_ALTP2M */
 
+#ifdef CONFIG_VMTRACE
 static inline int hvm_vmtrace_control(struct vcpu *v, bool enable, bool reset)
 {
     if ( hvm_funcs.vmtrace_control )
@@ -780,6 +783,12 @@ static inline int hvm_vmtrace_reset(struct vcpu *v)
 
     return -EOPNOTSUPP;
 }
+#else
+static inline int hvm_vmtrace_reset(struct vcpu *v)
+{
+    return 0;
+}
+#endif
 
 /*
  * Accessors for registers which have per-guest-type or per-vendor locations
diff --git a/xen/arch/x86/include/asm/hvm/vmx/vmcs.h 
b/xen/arch/x86/include/asm/hvm/vmx/vmcs.h
index 8ff7c8045fc6..d28a2682e9df 100644
--- a/xen/arch/x86/include/asm/hvm/vmx/vmcs.h
+++ b/xen/arch/x86/include/asm/hvm/vmx/vmcs.h
@@ -155,7 +155,9 @@ struct vmx_vcpu {
     bool                 ept_spurious_misconfig;
 
     /* Processor Trace configured and enabled for the vcpu. */
+#ifdef CONFIG_VMTRACE
     bool                 ipt_active;
+#endif
 
     /* Is the guest in real mode? */
     uint8_t              vmx_realmode;
diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
index 4787b2796479..074f1b2562b3 100644
--- a/xen/arch/x86/mm/mem_sharing.c
+++ b/xen/arch/x86/mm/mem_sharing.c
@@ -1888,7 +1888,9 @@ static int fork(struct domain *cd, struct domain *d)
         domain_pause(d);
         cd->max_pages = d->max_pages;
         *cd->arch.cpu_policy = *d->arch.cpu_policy;
+#ifdef CONFIG_VMTRACE
         cd->vmtrace_size = d->vmtrace_size;
+#endif
         cd->parent = d;
     }
 
diff --git a/xen/arch/x86/vm_event.c b/xen/arch/x86/vm_event.c
index fc349270b9c5..f4c8696ce54e 100644
--- a/xen/arch/x86/vm_event.c
+++ b/xen/arch/x86/vm_event.c
@@ -253,7 +253,9 @@ void vm_event_fill_regs(vm_event_request_t *req)
     req->data.regs.x86.shadow_gs = ctxt.shadow_gs;
     req->data.regs.x86.dr6 = ctxt.dr6;
 
+#ifdef CONFIG_VMTRACE
     if ( hvm_vmtrace_output_position(curr, &req->data.regs.x86.vmtrace_pos) != 
1 )
+#endif
         req->data.regs.x86.vmtrace_pos = ~0;
 #endif
 }
@@ -303,12 +305,12 @@ void vm_event_emulate_check(struct vcpu *v, 
vm_event_response_t *rsp)
 #endif
 }
 
+#ifdef CONFIG_VMTRACE
 void vm_event_reset_vmtrace(struct vcpu *v)
 {
-#ifdef CONFIG_HVM
     hvm_vmtrace_reset(v);
-#endif
 }
+#endif
 
 /*
  * Local variables:
diff --git a/xen/common/domain.c b/xen/common/domain.c
index 7dcd466e5a12..2be6ee03d004 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -136,7 +136,9 @@ struct vcpu *idle_vcpu[NR_CPUS] __read_mostly;
 
 vcpu_info_t dummy_vcpu_info;
 
+#ifdef CONFIG_VMTRACE
 bool __read_mostly vmtrace_available;
+#endif
 
 bool __read_mostly vpmu_is_available;
 
@@ -318,6 +320,7 @@ static void vcpu_info_reset(struct vcpu *v)
 
 static void vmtrace_free_buffer(struct vcpu *v)
 {
+#ifdef CONFIG_VMTRACE
     const struct domain *d = v->domain;
     struct page_info *pg = v->vmtrace.pg;
     unsigned int i;
@@ -332,10 +335,12 @@ static void vmtrace_free_buffer(struct vcpu *v)
         put_page_alloc_ref(&pg[i]);
         put_page_and_type(&pg[i]);
     }
+#endif
 }
 
 static int vmtrace_alloc_buffer(struct vcpu *v)
 {
+#ifdef CONFIG_VMTRACE
     struct domain *d = v->domain;
     struct page_info *pg;
     unsigned int i;
@@ -377,6 +382,9 @@ static int vmtrace_alloc_buffer(struct vcpu *v)
     }
 
     return -ENODATA;
+#else
+    return 0;
+#endif
 }
 
 /*
@@ -825,7 +833,9 @@ struct domain *domain_create(domid_t domid,
         ASSERT(!config->altp2m.nr);
 #endif
 
+#ifdef CONFIG_VMTRACE
         d->vmtrace_size = config->vmtrace_size;
+#endif
     }
 
     /* Sort out our idea of is_control_domain(). */
diff --git a/xen/common/memory.c b/xen/common/memory.c
index 3688e6dd5032..66dc7f7a0a41 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -1155,8 +1155,10 @@ static unsigned int resource_max_frames(const struct 
domain *d,
     case XENMEM_resource_ioreq_server:
         return ioreq_server_max_frames(d);
 
+#ifdef CONFIG_VMTRACE
     case XENMEM_resource_vmtrace_buf:
         return d->vmtrace_size >> PAGE_SHIFT;
+#endif
 
     default:
         return 0;
@@ -1198,6 +1200,7 @@ static int acquire_ioreq_server(struct domain *d,
 #endif
 }
 
+#ifdef CONFIG_VMTRACE
 static int acquire_vmtrace_buf(
     struct domain *d, unsigned int id, unsigned int frame,
     unsigned int nr_frames, xen_pfn_t mfn_list[])
@@ -1220,6 +1223,7 @@ static int acquire_vmtrace_buf(
 
     return nr_frames;
 }
+#endif
 
 /*
  * Returns -errno on error, or positive in the range [1, nr_frames] on
@@ -1238,8 +1242,10 @@ static int _acquire_resource(
     case XENMEM_resource_ioreq_server:
         return acquire_ioreq_server(d, id, frame, nr_frames, mfn_list);
 
+#ifdef CONFIG_VMTRACE
     case XENMEM_resource_vmtrace_buf:
         return acquire_vmtrace_buf(d, id, frame, nr_frames, mfn_list);
+#endif
 
     default:
         ASSERT_UNREACHABLE();
diff --git a/xen/common/vm_event.c b/xen/common/vm_event.c
index b2787c010890..cf0258223f50 100644
--- a/xen/common/vm_event.c
+++ b/xen/common/vm_event.c
@@ -441,7 +441,8 @@ static int vm_event_resume(struct domain *d, struct 
vm_event_domain *ved)
             if ( rsp.flags & VM_EVENT_FLAG_GET_NEXT_INTERRUPT )
                 vm_event_monitor_next_interrupt(v);
 
-            if ( rsp.flags & VM_EVENT_FLAG_RESET_VMTRACE )
+            if ( IS_ENABLED(CONFIG_VMTRACE) &&
+                 (rsp.flags & VM_EVENT_FLAG_RESET_VMTRACE) )
                 vm_event_reset_vmtrace(v);
 
             if ( rsp.flags & VM_EVENT_FLAG_VCPU_PAUSED )
diff --git a/xen/include/xen/domain.h b/xen/include/xen/domain.h
index 8aab05ae93c8..aa86a9f46022 100644
--- a/xen/include/xen/domain.h
+++ b/xen/include/xen/domain.h
@@ -191,7 +191,11 @@ void vnuma_destroy(struct vnuma_info *vnuma);
 static inline void vnuma_destroy(struct vnuma_info *vnuma) { ASSERT(!vnuma); }
 #endif
 
+#ifdef CONFIG_VMTRACE
 extern bool vmtrace_available;
+#else
+#define vmtrace_available false
+#endif
 
 extern bool vpmu_is_available;
 
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 02bdc256ce37..dcd8647e0d36 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -300,9 +300,11 @@ struct vcpu
     /* vPCI per-vCPU area, used to store data for long running operations. */
     struct vpci_vcpu vpci;
 
+#ifdef CONFIG_VMTRACE
     struct {
         struct page_info *pg; /* One contiguous allocation of d->vmtrace_size 
*/
     } vmtrace;
+#endif
 
     struct arch_vcpu arch;
 
@@ -623,7 +625,9 @@ struct domain
     unsigned int nr_altp2m;    /* Number of altp2m tables. */
 #endif
 
+#ifdef CONFIG_VMTRACE
     unsigned int vmtrace_size; /* Buffer size in bytes, or 0 to disable. */
+#endif
 
 #ifdef CONFIG_ARGO
     /* Argo interdomain communication support */
-- 
2.34.1



 


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