[Xen-devel] [PATCH RFC V2 2/6] xen: Optimize introspection access to guest state

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

Speed optimization for introspection purposes: a handful of registers
are sent along with each mem_event. This requires enlargement of the
mem_event_request / mem_event_response stuctures, and additional code
to fill in relevant values. Since the EPT event processing code needs
more data than CR3 or MSR event processors, hvm_mem_event_fill_regs()
fills in less data than p2m_mem_event_fill_regs(), in order to avoid
overhead. Struct hvm_hw_cpu has been considered instead of the custom
struct mem_event_regs_st, but its size would cause quick filling up
of the mem_event ring buffer.

Changes since V1:
 - Replaced guest_x86_mode with cs_arbytes in the mem_event_regs_st
   structure.
 - Removed superfluous preprocessor check for __x86_64__ in
   p2m_mem_event_fill_regs().

Signed-off-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
---
 xen/arch/x86/hvm/hvm.c         |   33 ++++++++++++++++++++++
 xen/arch/x86/mm/p2m.c          |   60 ++++++++++++++++++++++++++++++++++++++++
 xen/include/public/mem_event.h |   38 +++++++++++++++++++++++++
 3 files changed, 131 insertions(+)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index ef2411c..89a0382 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -6085,6 +6085,38 @@ int hvm_debug_op(struct vcpu *v, int32_t op)
     return rc;
 }
 
+static inline void hvm_mem_event_fill_regs(mem_event_request_t *req)
+{
+    struct cpu_user_regs *regs = guest_cpu_user_regs();
+    struct vcpu *v = current;
+
+    req->regs.rax = regs->eax;
+    req->regs.rcx = regs->ecx;
+    req->regs.rdx = regs->edx;
+    req->regs.rbx = regs->ebx;
+    req->regs.rsp = regs->esp;
+    req->regs.rbp = regs->ebp;
+    req->regs.rsi = regs->esi;
+    req->regs.rdi = regs->edi;
+
+    req->regs.r8  = regs->r8;
+    req->regs.r9  = regs->r9;
+    req->regs.r10 = regs->r10;
+    req->regs.r11 = regs->r11;
+    req->regs.r12 = regs->r12;
+    req->regs.r13 = regs->r13;
+    req->regs.r14 = regs->r14;
+    req->regs.r15 = regs->r15;
+
+    req->regs.rflags = regs->eflags;
+    req->regs.rip    = regs->eip;
+
+    req->regs.msr_efer = v->arch.hvm_vcpu.guest_efer;
+    req->regs.cr0 = v->arch.hvm_vcpu.guest_cr[0];
+    req->regs.cr3 = v->arch.hvm_vcpu.guest_cr[3];
+    req->regs.cr4 = v->arch.hvm_vcpu.guest_cr[4];
+}
+
 static int hvm_memory_event_traps(long p, uint32_t reason,
                                   unsigned long value, unsigned long old, 
                                   bool_t gla_valid, unsigned long gla) 
@@ -6129,6 +6161,7 @@ static int hvm_memory_event_traps(long p, uint32_t reason,
         req.gla = old;
     }
     
+    hvm_mem_event_fill_regs(&req);
     mem_event_put_request(d, &d->mem_event->access, &req);
     
     return 1;
diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 642ec28..13fdf78 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -1314,6 +1314,63 @@ void p2m_mem_paging_resume(struct domain *d)
     }
 }
 
+static inline void p2m_mem_event_fill_regs(mem_event_request_t *req)
+{
+    struct cpu_user_regs *regs = guest_cpu_user_regs();
+    struct segment_register seg;
+    struct hvm_hw_cpu ctxt;
+    struct vcpu *v = current;
+
+    memset(&ctxt, 0, sizeof(struct hvm_hw_cpu));
+
+    /* Architecture-specific vmcs/vmcb bits */
+    hvm_funcs.save_cpu_ctxt(v, &ctxt);
+
+    req->regs.rax = regs->eax;
+    req->regs.rcx = regs->ecx;
+    req->regs.rdx = regs->edx;
+    req->regs.rbx = regs->ebx;
+    req->regs.rsp = regs->esp;
+    req->regs.rbp = regs->ebp;
+    req->regs.rsi = regs->esi;
+    req->regs.rdi = regs->edi;
+
+    req->regs.r8  = regs->r8;
+    req->regs.r9  = regs->r9;
+    req->regs.r10 = regs->r10;
+    req->regs.r11 = regs->r11;
+    req->regs.r12 = regs->r12;
+    req->regs.r13 = regs->r13;
+    req->regs.r14 = regs->r14;
+    req->regs.r15 = regs->r15;
+
+    req->regs.rflags = regs->eflags;
+    req->regs.rip    = regs->eip;
+
+    req->regs.dr7 = v->arch.debugreg[7];
+    req->regs.cr0 = ctxt.cr0;
+    req->regs.cr2 = ctxt.cr2;
+    req->regs.cr3 = ctxt.cr3;
+    req->regs.cr4 = ctxt.cr4;
+
+    req->regs.sysenter_cs = ctxt.sysenter_cs;
+    req->regs.sysenter_esp = ctxt.sysenter_esp;
+    req->regs.sysenter_eip = ctxt.sysenter_eip;
+
+    req->regs.msr_efer = ctxt.msr_efer;
+    req->regs.msr_star = ctxt.msr_star;
+    req->regs.msr_lstar = ctxt.msr_lstar;
+
+    hvm_get_segment_register(v, x86_seg_fs, &seg);
+    req->regs.fs_base = seg.base;
+
+    hvm_get_segment_register(v, x86_seg_gs, &seg);
+    req->regs.gs_base = seg.base;
+
+    hvm_get_segment_register(v, x86_seg_cs, &seg);
+    req->regs.cs_arbytes = seg.attr.bytes;;
+}
+
 bool_t p2m_mem_access_check(paddr_t gpa, bool_t gla_valid, unsigned long gla, 
                           bool_t access_r, bool_t access_w, bool_t access_x,
                           mem_event_request_t **req_ptr)
@@ -1407,6 +1464,9 @@ bool_t p2m_mem_access_check(paddr_t gpa, bool_t 
gla_valid, unsigned long gla,
     if ( p2ma != p2m_access_n2rwx )
         vcpu_pause_nosync(v);
 
+    if ( req )
+        p2m_mem_event_fill_regs(req);
+
     /* VCPU may be paused, return whether we promoted automatically */
     return (p2ma == p2m_access_n2rwx);
 }
diff --git a/xen/include/public/mem_event.h b/xen/include/public/mem_event.h
index 3831b41..b9af728 100644
--- a/xen/include/public/mem_event.h
+++ b/xen/include/public/mem_event.h
@@ -48,6 +48,43 @@
 #define MEM_EVENT_REASON_MSR         7    /* MSR was hit: gfn is MSR value, 
gla is MSR address;
                                              does NOT honour 
HVMPME_onchangeonly */
 
+/* Using a custom struct (not hvm_hw_cpu) so as to not fill
+ * the mem_event ring buffer too quickly. */
+typedef struct mem_event_regs_st {
+    uint64_t rax;
+    uint64_t rcx;
+    uint64_t rdx;
+    uint64_t rbx;
+    uint64_t rsp;
+    uint64_t rbp;
+    uint64_t rsi;
+    uint64_t rdi;
+    uint64_t r8;
+    uint64_t r9;
+    uint64_t r10;
+    uint64_t r11;
+    uint64_t r12;
+    uint64_t r13;
+    uint64_t r14;
+    uint64_t r15;
+    uint64_t rflags;
+    uint64_t dr7;
+    uint64_t rip;
+    uint64_t cr0;
+    uint64_t cr2;
+    uint64_t cr3;
+    uint64_t cr4;
+    uint64_t sysenter_cs;
+    uint64_t sysenter_esp;
+    uint64_t sysenter_eip;
+    uint64_t msr_efer;
+    uint64_t msr_star;
+    uint64_t msr_lstar;
+    uint64_t fs_base;
+    uint64_t gs_base;
+    uint32_t cs_arbytes;
+} mem_event_regs_t;
+
 typedef struct mem_event_st {
     uint32_t flags;
     uint32_t vcpu_id;
@@ -65,6 +102,7 @@ typedef struct mem_event_st {
     uint16_t available:12;
 
     uint16_t reason;
+    mem_event_regs_t regs;
 } mem_event_request_t, mem_event_response_t;
 
 DEFINE_RING_TYPES(mem_event, mem_event_request_t, mem_event_response_t);
-- 
1.7.9.5


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