[RFC v2 09/32] x86/tdx: Add HLT support for TDX guest

[Kuppuswamy Sathyanarayanan]

From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>

Per Guest-Host-Communication Interface (GHCI) for Intel Trust
Domain Extensions (Intel TDX) specification, sec 3.8,
TDVMCALL[Instruction.HLT] provides HLT operation. Use it to implement
halt() and safe_halt() paravirtualization calls.

The same TDVMCALL is used to handle #VE exception due to
EXIT_REASON_HLT.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reviewed-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
---
 arch/x86/kernel/tdx.c | 44 ++++++++++++++++++++++++++++++++++++-------
 1 file changed, 37 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
index ccfcb07bfb2c..5169f72b6b3f 100644
--- a/arch/x86/kernel/tdx.c
+++ b/arch/x86/kernel/tdx.c
@@ -82,6 +82,27 @@ static void tdg_get_info(void)
 	td_info.attributes = out.rdx;
 }
 
+static __cpuidle void tdg_halt(void)
+{
+	u64 ret;
+
+	ret = __tdvmcall(EXIT_REASON_HLT, 0, 0, 0, 0, NULL);
+
+	/* It should never fail */
+	BUG_ON(ret);
+}
+
+static __cpuidle void tdg_safe_halt(void)
+{
+	/*
+	 * Enable interrupts next to the TDVMCALL to avoid
+	 * performance degradation.
+	 */
+	asm volatile("sti\n\t");
+
+	tdg_halt();
+}
+
 unsigned long tdg_get_ve_info(struct ve_info *ve)
 {
 	u64 ret;
@@ -111,13 +132,19 @@ unsigned long tdg_get_ve_info(struct ve_info *ve)
 int tdg_handle_virtualization_exception(struct pt_regs *regs,
 		struct ve_info *ve)
 {
-	/*
-	 * TODO: Add handler support for various #VE exit
-	 * reasons. It will be added by other patches in
-	 * the series.
-	 */
-	pr_warn("Unexpected #VE: %lld\n", ve->exit_reason);
-	return -EFAULT;
+	switch (ve->exit_reason) {
+	case EXIT_REASON_HLT:
+		tdg_halt();
+		break;
+	default:
+		pr_warn("Unexpected #VE: %lld\n", ve->exit_reason);
+		return -EFAULT;
+	}
+
+	/* After successful #VE handling, move the IP */
+	regs->ip += ve->instr_len;
+
+	return 0;
 }
 
 void __init tdx_early_init(void)
@@ -129,5 +156,8 @@ void __init tdx_early_init(void)
 
 	tdg_get_info();
 
+	pv_ops.irq.safe_halt = tdg_safe_halt;
+	pv_ops.irq.halt = tdg_halt;
+
 	pr_info("TDX guest is initialized\n");
 }
-- 
2.25.1