[Xen-devel] [PATCH 2/3] x86: also show FS/GS base addresses when dumping registers

["Jan Beulich" <JBeulich@xxxxxxxx>]

Their state may be important to figure the reason for a crash. To not
further grow duplicate code, break out a helper function.

I realize that (ab)using the control register array here may not be
considered the nicest solution, but it seems easier (and less overall
overhead) to do so compared to the alternative of introducing another
helper structure.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/x86_64/traps.c
+++ b/xen/arch/x86/x86_64/traps.c
@@ -36,6 +36,21 @@ static void print_xen_info(void)
 
 enum context { CTXT_hypervisor, CTXT_pv_guest, CTXT_hvm_guest };
 
+static void read_registers(struct cpu_user_regs *regs, unsigned long crs[8])
+{
+    crs[0] = read_cr0();
+    crs[2] = read_cr2();
+    crs[3] = read_cr3();
+    crs[4] = read_cr4();
+    regs->ds = read_sreg(ds);
+    regs->es = read_sreg(es);
+    regs->fs = read_sreg(fs);
+    regs->gs = read_sreg(gs);
+    crs[5] = rdfsbase();
+    crs[6] = rdgsbase();
+    rdmsrl(MSR_SHADOW_GS_BASE, crs[7]);
+}
+
 static void _show_registers(
     const struct cpu_user_regs *regs, unsigned long crs[8],
     enum context context, const struct vcpu *v)
@@ -74,6 +89,8 @@ static void _show_registers(
     else
         printk("cr0: %016lx   cr4: %016lx\n", crs[0], crs[4]);
     printk("cr3: %016lx   cr2: %016lx\n", crs[3], crs[2]);
+    printk("fsb: %016lx   gsb: %016lx   gss: %016lx\n",
+           crs[5], crs[6], crs[7]);
     printk("ds: %04x   es: %04x   fs: %04x   gs: %04x   "
            "ss: %04x   cs: %04x\n",
            regs->ds, regs->es, regs->fs,
@@ -103,13 +120,18 @@ void show_registers(const struct cpu_use
         fault_regs.es = sreg.sel;
         hvm_get_segment_register(v, x86_seg_fs, &sreg);
         fault_regs.fs = sreg.sel;
+        fault_crs[5] = sreg.base;
         hvm_get_segment_register(v, x86_seg_gs, &sreg);
         fault_regs.gs = sreg.sel;
+        fault_crs[6] = sreg.base;
         hvm_get_segment_register(v, x86_seg_ss, &sreg);
         fault_regs.ss = sreg.sel;
+        fault_crs[7] = hvm_get_shadow_gs_base(v);
     }
     else
     {
+        read_registers(&fault_regs, fault_crs);
+
         if ( guest_mode(regs) )
         {
             context = CTXT_pv_guest;
@@ -120,14 +142,6 @@ void show_registers(const struct cpu_use
             context = CTXT_hypervisor;
             fault_crs[2] = read_cr2();
         }
-
-        fault_crs[0] = read_cr0();
-        fault_crs[3] = read_cr3();
-        fault_crs[4] = read_cr4();
-        fault_regs.ds = read_sreg(ds);
-        fault_regs.es = read_sreg(es);
-        fault_regs.fs = read_sreg(fs);
-        fault_regs.gs = read_sreg(gs);
     }
 
     print_xen_info();
@@ -146,6 +160,7 @@ void show_registers(const struct cpu_use
 void vcpu_show_registers(const struct vcpu *v)
 {
     const struct cpu_user_regs *regs = &v->arch.user_regs;
+    bool_t kernel = guest_kernel_mode(v, regs);
     unsigned long crs[8];
 
     /* Only handle PV guests for now */
@@ -154,10 +169,13 @@ void vcpu_show_registers(const struct vc
 
     crs[0] = v->arch.pv_vcpu.ctrlreg[0];
     crs[2] = arch_get_cr2(v);
-    crs[3] = pagetable_get_paddr(guest_kernel_mode(v, regs) ?
+    crs[3] = pagetable_get_paddr(kernel ?
                                  v->arch.guest_table :
                                  v->arch.guest_table_user);
     crs[4] = v->arch.pv_vcpu.ctrlreg[4];
+    crs[5] = v->arch.pv_vcpu.fs_base;
+    crs[6 + !kernel] = v->arch.pv_vcpu.gs_base_kernel;
+    crs[7 - !kernel] = v->arch.pv_vcpu.gs_base_user;
 
     _show_registers(regs, crs, CTXT_pv_guest, v);
 }
@@ -237,14 +255,7 @@ void do_double_fault(struct cpu_user_reg
     printk("*** DOUBLE FAULT ***\n");
     print_xen_info();
 
-    crs[0] = read_cr0();
-    crs[2] = read_cr2();
-    crs[3] = read_cr3();
-    crs[4] = read_cr4();
-    regs->ds = read_sreg(ds);
-    regs->es = read_sreg(es);
-    regs->fs = read_sreg(fs);
-    regs->gs = read_sreg(gs);
+    read_registers(regs, crs);
 
     printk("CPU:    %d\n", cpu);
     _show_registers(regs, crs, CTXT_hypervisor, NULL);



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