On Mon, Oct 04, 2021 at 07:52:01PM -0700, Kuppuswamy Sathyanarayanan wrote:
@@ -240,6 +243,33 @@ SYM_FUNC_START(__tdx_hypercall)
movl $TDVMCALL_EXPOSE_REGS_MASK, %ecx
+ /*
+ * For the idle loop STI needs to be called directly before
+ * the TDCALL that enters idle (EXIT_REASON_HLT case). STI
+ * enables interrupts only one instruction later. If there
+ * are any instructions between the STI and the TDCALL for
+ * HLT then an interrupt could happen in that time, but the
+ * code would go back to sleep afterwards, which can cause
+ * longer delays.
+ *
+ * This leads to significant difference in network performance
+ * benchmarks. So add a special case for EXIT_REASON_HLT to
+ * trigger STI before TDCALL. But this change is not required
+ * for all HLT cases. So use R15 register value to identify the
+ * case which needs STI. So, if R11 is EXIT_REASON_HLT and R15
+ * is 1, then call STI before TDCALL instruction. Note that R15
+ * register is not required by TDCALL ABI when triggering the
+ * hypercall for EXIT_REASON_HLT case. So use it in software to
+ * select the STI case.
+ */
+ cmpl $EXIT_REASON_HLT, %r11d
+ jne skip_sti
+ cmpl $1, %r15d
+ jne skip_sti
+ /* Set R15 register to 0, it is unused in EXIT_REASON_HLT case */
+ xor %r15, %r15
Then you don't need to clear it either, right?
+ sti
+skip_sti:
tdcall
/* Restore output pointer to R9 */
...
+static __cpuidle void tdx_halt(void)
+{
+ const bool irq_disabled = irqs_disabled();
+ const bool do_sti = false;
+
+ /*
+ * Non safe halt is mainly used in CPU off-lining
+ * and the guest will stay in halt state. So,
+ * STI instruction call is not required (set
+ * do_sti as false).
+ */
Just like you've done below, put the comment over the variable assignment:
/*
* Non safe halt is mainly used in CPU offlining and the guest will stay in halt
* state. So, STI instruction call is not required.
*/
const bool do_sti = false;
+ _tdx_halt(irq_disabled, do_sti);
+}
+
+static __cpuidle void tdx_safe_halt(void)
+{
+ /*
+ * Since STI instruction will be called in __tdx_hypercall()
+ * set irq_disabled as false.
+ */
+ const bool irq_disabled = false;
+ const bool do_sti = true;
+
+ _tdx_halt(irq_disabled, do_sti);
+}
+
unsigned long tdx_get_ve_info(struct ve_info *ve)
{
struct tdx_module_output out = {0};