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x86/tdx: Remove TDX_HCALL_ISSUE_STI

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Now that arch_cpu_idle() is expected to return with IRQs disabled,
avoid the useless STI/CLI dance.

Per the specs this is supposed to work, but nobody has yet relied up
this behaviour so broken implementations are possible.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Tony Lindgren <tony@atomide.com>
Tested-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20230112195540.682137572@infradead.org
This commit is contained in:
Peter Zijlstra 2023-01-12 20:43:36 +01:00 committed by Ingo Molnar
parent 89b3098703
commit e80a48bade
3 changed files with 4 additions and 33 deletions
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13
arch/x86/coco/tdx/tdcall.S
View File

@ -139,19 +139,6 @@ 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 instruction enables
* interrupts only one instruction later. If there is a window between
* STI and the instruction that emulates the HALT state, there is a
* chance for interrupts to happen in this window, which can delay the
* HLT operation indefinitely. Since this is the not the desired
* result, conditionally call STI before TDCALL.
*/
testq $TDX_HCALL_ISSUE_STI, %rsi
jz .Lskip_sti
sti
.Lskip_sti:
tdcall
/*

23
arch/x86/coco/tdx/tdx.c
View File

@ -220,7 +220,7 @@ static int ve_instr_len(struct ve_info *ve)
}
}
static u64 __cpuidle __halt(const bool irq_disabled, const bool do_sti)
static u64 __cpuidle __halt(const bool irq_disabled)
{
struct tdx_hypercall_args args = {
.r10 = TDX_HYPERCALL_STANDARD,
@ -240,20 +240,14 @@ static u64 __cpuidle __halt(const bool irq_disabled, const bool do_sti)
* can keep the vCPU in virtual HLT, even if an IRQ is
* pending, without hanging/breaking the guest.
*/
return __tdx_hypercall(&args, do_sti ? TDX_HCALL_ISSUE_STI : 0);
return __tdx_hypercall(&args, 0);
}
static int handle_halt(struct ve_info *ve)
{
/*
* Since non safe halt is mainly used in CPU offlining
* and the guest will always stay in the halt state, don't
* call the STI instruction (set do_sti as false).
*/
const bool irq_disabled = irqs_disabled();
const bool do_sti = false;
if (__halt(irq_disabled, do_sti))
if (__halt(irq_disabled))
return -EIO;
return ve_instr_len(ve);
@ -261,22 +255,13 @@ static int handle_halt(struct ve_info *ve)
void __cpuidle tdx_safe_halt(void)
{
/*
* For do_sti=true case, __tdx_hypercall() function enables
* interrupts using the STI instruction before the TDCALL. So
* set irq_disabled as false.
*/
const bool irq_disabled = false;
const bool do_sti = true;
/*
* Use WARN_ONCE() to report the failure.
*/
if (__halt(irq_disabled, do_sti))
if (__halt(irq_disabled))
WARN_ONCE(1, "HLT instruction emulation failed\n");
/* XXX I can't make sense of what @do_sti actually does */
raw_local_irq_disable();
}
static int read_msr(struct pt_regs *regs, struct ve_info *ve)

1
arch/x86/include/asm/shared/tdx.h
View File

@ -8,7 +8,6 @@
#define TDX_HYPERCALL_STANDARD 0
#define TDX_HCALL_HAS_OUTPUT BIT(0)
#define TDX_HCALL_ISSUE_STI BIT(1)
#define TDX_CPUID_LEAF_ID 0x21
#define TDX_IDENT "IntelTDX "