[v5,1/3] x86/cpufeatures: Add CPUID feature bit for Idle HLT intercept

Commit Message

Manali Shukla Jan. 3, 2025, 8:18 a.m. UTC

From: Manali Shukla <[e-mail]>

The Idle HLT Intercept feature allows for the HLT instruction
execution by a vCPU to be intercepted by the hypervisor only if there
are no pending events (V_INTR and V_NMI) for the vCPU. When the vCPU
is expected to service the pending events (V_INTR and V_NMI), the Idle
HLT intercept won’t trigger. The feature allows the hypervisor to
determine if the vCPU is idle and reduces wasteful VMEXITs.

In addition to the aforementioned use case, the Idle HLT intercept
feature is also used for enlightened guests who aim to securely manage
events without the hypervisor’s awareness. If a HLT occurs while
a virtual event is pending and the hypervisor is unaware of this
pending event (as could be the case with enlightened guests), the
absence of the Idle HLT intercept feature could result in a vCPU being
suspended indefinitely.

Presence of Idle HLT intercept feature for guests is indicated via CPUID
function 0x8000000A_EDX[30].

Signed-off-by: Manali Shukla <[e-mail]>
Acked-by: Borislav Petkov (AMD) <[e-mail]>
---
 arch/x86/include/asm/cpufeatures.h | 1 +
 1 file changed, 1 insertion(+)


base-commit: 13e98294d7cec978e31138d16824f50556a62d17
prerequisite-patch-id: cb345fc0d814a351df2b5788b76eee0eef9de549
prerequisite-patch-id: 71806f400cffe09f47d6231cb072cbdbd540de1b
prerequisite-patch-id: 9ea0412aab7ecd8555fcee3e9609dbfe8456d47b
prerequisite-patch-id: 3504df50cdd33958456f2e56139d76867273525c
prerequisite-patch-id: 674e56729a56cc487cb85be1a64ef561eb7bac8a
prerequisite-patch-id: 48e87354f9d6e6bd121ca32ab73cd0d7f1dce74f
prerequisite-patch-id: 74daffd7677992995f37e5a5cb784b8d4357e342
prerequisite-patch-id: 509018dc2fc1657debc641544e86f5a92d04bc1a
prerequisite-patch-id: 4a50c6a4dc3b3c8c8c640a86072faafb7bae4384

Patch

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 645aa360628d..4fef0533f764 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -386,6 +386,7 @@ 
 #define X86_FEATURE_V_SPEC_CTRL		(15*32+20) /* "v_spec_ctrl" Virtual SPEC_CTRL */
 #define X86_FEATURE_VNMI		(15*32+25) /* "vnmi" Virtual NMI */
 #define X86_FEATURE_SVME_ADDR_CHK	(15*32+28) /* SVME addr check */
+#define X86_FEATURE_IDLE_HLT		(15*32+30) /* IDLE HLT intercept */
 
 /* Intel-defined CPU features, CPUID level 0x00000007:0 (ECX), word 16 */
 #define X86_FEATURE_AVX512VBMI		(16*32+ 1) /* "avx512vbmi" AVX512 Vector Bit Manipulation instructions*/