Messages in this thread | | | Date | Fri, 8 Oct 2021 19:31:36 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v8 07/11] x86/tdx: Add HLT support for TDX guest |
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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};
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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