Direct HLT instruction execution causes #VEs for TDX VMs which is routed
to hypervisor via TDCALL. safe_halt() routines execute HLT in STI-shadow
so IRQs need to remain disabled until the TDCALL to ensure that pending
IRQs are correctly treated as wake events. So "sti;hlt" sequence needs to
be replaced for TDX VMs with "TDCALL; *_irq_enable()" to keep interrupts
disabled during TDCALL execution.
Commit bfe6ed0c6727 ("x86/tdx: Add HLT support for TDX guests")
prevented the idle routines from using "sti;hlt". But it missed the
paravirt routine which can be reached like this as an example:
acpi_safe_halt() =>
raw_safe_halt() =>
arch_safe_halt() =>
irq.safe_halt() =>
pv_native_safe_halt()
Modify tdx_safe_halt() to implement the sequence "TDCALL;
raw_local_irq_enable()" and invoke tdx_halt() from idle routine which just
executes TDCALL without toggling interrupt state. Introduce dependency
on CONFIG_PARAVIRT and override paravirt halt()/safe_halt() routines for
TDX VMs.
Cc: sta...@vger.kernel.org
Fixes: bfe6ed0c6727 ("x86/tdx: Add HLT support for TDX guests")
Signed-off-by: Vishal Annapurve <vannapu...@google.com>
---
arch/x86/Kconfig | 1 +
arch/x86/coco/tdx/tdx.c | 22 +++++++++++++++++++++-
arch/x86/include/asm/tdx.h | 2 +-
arch/x86/kernel/process.c | 2 +-
4 files changed, 24 insertions(+), 3 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 87198d957e2f..afcdbc9693dc 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -902,6 +902,7 @@ config INTEL_TDX_GUEST
depends on X86_64 && CPU_SUP_INTEL
depends on X86_X2APIC
depends on EFI_STUB
+ depends on PARAVIRT
select ARCH_HAS_CC_PLATFORM
select X86_MEM_ENCRYPT
select X86_MCE
diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 32809a06dab4..7ab427e85bd3 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -14,6 +14,7 @@
#include <asm/ia32.h>
#include <asm/insn.h>
#include <asm/insn-eval.h>
+#include <asm/paravirt_types.h>
#include <asm/pgtable.h>
#include <asm/set_memory.h>
#include <asm/traps.h>
@@ -398,7 +399,7 @@ static int handle_halt(struct ve_info *ve)
return ve_instr_len(ve);
}
-void __cpuidle tdx_safe_halt(void)
+void __cpuidle tdx_halt(void)
{
const bool irq_disabled = false;
@@ -409,6 +410,16 @@ void __cpuidle tdx_safe_halt(void)
WARN_ONCE(1, "HLT instruction emulation failed\n");
}
+static void __cpuidle tdx_safe_halt(void)
+{
+ tdx_halt();
+ /*
+ * "__cpuidle" section doesn't support instrumentation, so stick
+ * with raw_* variant that avoids tracing hooks.
+ */
+ raw_local_irq_enable();
+}
+
static int read_msr(struct pt_regs *regs, struct ve_info *ve)
{
struct tdx_module_args args = {
@@ -1109,6 +1120,15 @@ void __init tdx_early_init(void)
x86_platform.guest.enc_kexec_begin = tdx_kexec_begin;
x86_platform.guest.enc_kexec_finish = tdx_kexec_finish;
+ /*
+ * "sti;hlt" execution in TDX guests will induce a #VE in the STI-shadow
+ * which will enable interrupts before HLT TDCALL inocation possibly
+ * resulting in missed wakeup events. Modify all possible HLT
+ * execution paths to use TDCALL for performance/reliability reasons.
+ */
+ pv_ops.irq.safe_halt = tdx_safe_halt;
+ pv_ops.irq.halt = tdx_halt;
+
/*
* TDX intercepts the RDMSR to read the X2APIC ID in the parallel
* bringup low level code. That raises #VE which cannot be handled
diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index b4b16dafd55e..393ee2dfaab1 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -58,7 +58,7 @@ void tdx_get_ve_info(struct ve_info *ve);
bool tdx_handle_virt_exception(struct pt_regs *regs, struct ve_info *ve);
-void tdx_safe_halt(void);
+void tdx_halt(void);
bool tdx_early_handle_ve(struct pt_regs *regs);
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 6da6769d7254..d11956a178df 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -934,7 +934,7 @@ void __init select_idle_routine(void)
static_call_update(x86_idle, mwait_idle);
} else if (cpu_feature_enabled(X86_FEATURE_TDX_GUEST)) {
pr_info("using TDX aware idle routine\n");
- static_call_update(x86_idle, tdx_safe_halt);
+ static_call_update(x86_idle, tdx_halt);
} else {
static_call_update(x86_idle, default_idle);
}
--
2.48.1.601.g30ceb7b040-goog
