x86/tdx: Remove TDX_HCALL_ISSUE_STI

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

diff --git a/arch/x86/coco/tdx/tdcall.S b/arch/x86/coco/tdx/tdcall.S
index f9eb1134f22defc1c7e69ce28bc6efabb0bf82f9..508c17332e2ecb4323321f7fb40bcc4e37a61777 100644 (file)
--- a/arch/x86/coco/tdx/tdcall.S
+++ b/arch/x86/coco/tdx/tdcall.S
@@ -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
 
        /*

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index f4a59c365321c6f12c70865d656cde65fff42a04..8804174aef1a22f9101daeae267c6f907d1ddeaf 100644 (file)
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -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)

diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h
index e53f26228fbbd91e0511fc34add1e6290ea4b84c..559176887791ea6668f0707a8551a84dea77a7f9 100644 (file)
--- a/arch/x86/include/asm/shared/tdx.h
+++ b/arch/x86/include/asm/shared/tdx.h
@@ -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    "