[Xen-devel] [PATCH 1 of 2 V4] x86/IST: Create set_ist() helper function

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

 xen/arch/x86/hvm/svm/svm.c      |  12 ++++++------
 xen/arch/x86/x86_64/traps.c     |   6 +++---
 xen/include/asm-x86/processor.h |  18 ++++++++++++++----
 3 files changed, 23 insertions(+), 13 deletions(-)


... to save using open-coded bitwise operations, and update all IST
manipulation sites to use the function.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

--

Changes since v1:
 * Change ASSERT() to assert against IST_MAX, the maximum Xen used IST
   value, rather than the maximum possible IST value.
 * Removed second '& 7UL' as it would be optimised out in all acceptable
   use cases.

diff -r bc624b00d6d6 -r def9d03429f6 xen/arch/x86/hvm/svm/svm.c
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -869,9 +869,9 @@ static void svm_ctxt_switch_from(struct 
     svm_vmload(per_cpu(root_vmcb, cpu));
 
     /* Resume use of ISTs now that the host TR is reinstated. */
-    idt_tables[cpu][TRAP_double_fault].a  |= IST_DF << 32;
-    idt_tables[cpu][TRAP_nmi].a           |= IST_NMI << 32;
-    idt_tables[cpu][TRAP_machine_check].a |= IST_MCE << 32;
+    set_ist(&idt_tables[cpu][TRAP_double_fault],  IST_DF);
+    set_ist(&idt_tables[cpu][TRAP_nmi],           IST_NMI);
+    set_ist(&idt_tables[cpu][TRAP_machine_check], IST_MCE);
 }
 
 static void svm_ctxt_switch_to(struct vcpu *v)
@@ -893,9 +893,9 @@ static void svm_ctxt_switch_to(struct vc
      * Cannot use ISTs for NMI/#MC/#DF while we are running with the guest TR.
      * But this doesn't matter: the IST is only req'd to handle SYSCALL/SYSRET.
      */
-    idt_tables[cpu][TRAP_double_fault].a  &= ~(7UL << 32);
-    idt_tables[cpu][TRAP_nmi].a           &= ~(7UL << 32);
-    idt_tables[cpu][TRAP_machine_check].a &= ~(7UL << 32);
+    set_ist(&idt_tables[cpu][TRAP_double_fault],  IST_NONE);
+    set_ist(&idt_tables[cpu][TRAP_nmi],           IST_NONE);
+    set_ist(&idt_tables[cpu][TRAP_machine_check], IST_NONE);
 
     svm_restore_dr(v);
 
diff -r bc624b00d6d6 -r def9d03429f6 xen/arch/x86/x86_64/traps.c
--- a/xen/arch/x86/x86_64/traps.c
+++ b/xen/arch/x86/x86_64/traps.c
@@ -370,9 +370,9 @@ void __devinit subarch_percpu_traps_init
     {
         /* Specify dedicated interrupt stacks for NMI, #DF, and #MC. */
         set_intr_gate(TRAP_double_fault, &double_fault);
-        idt_table[TRAP_double_fault].a  |= IST_DF << 32;
-        idt_table[TRAP_nmi].a           |= IST_NMI << 32;
-        idt_table[TRAP_machine_check].a |= IST_MCE << 32;
+        set_ist(&idt_table[TRAP_double_fault],  IST_DF);
+        set_ist(&idt_table[TRAP_nmi],           IST_NMI);
+        set_ist(&idt_table[TRAP_machine_check], IST_MCE);
 
         /*
          * The 32-on-64 hypercall entry vector is only accessible from ring 1.
diff -r bc624b00d6d6 -r def9d03429f6 xen/include/asm-x86/processor.h
--- a/xen/include/asm-x86/processor.h
+++ b/xen/include/asm-x86/processor.h
@@ -425,10 +425,20 @@ struct tss_struct {
     u8 __cacheline_filler[24];
 } __cacheline_aligned __attribute__((packed));
 
-#define IST_DF  1UL
-#define IST_NMI 2UL
-#define IST_MCE 3UL
-#define IST_MAX 3UL
+#define IST_NONE 0UL
+#define IST_DF   1UL
+#define IST_NMI  2UL
+#define IST_MCE  3UL
+#define IST_MAX  3UL
+
+/* Set the interrupt stack table used by a particular interrupt
+ * descriptor table entry. */
+static always_inline void set_ist(idt_entry_t * idt, unsigned long ist)
+{
+    /* ist is a 3 bit field, 32 bits into the idt entry. */
+    ASSERT( ist <= IST_MAX );
+    idt->a = ( idt->a & ~(7UL << 32) ) | ( ist << 32 );
+}
 
 #define IDT_ENTRIES 256
 extern idt_entry_t idt_table[];

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