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Subject[RFC v1 06/26] x86/tdx: Add HLT support for TDX guest
Date
From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>

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@linux.intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
---
arch/x86/include/asm/tdx.h | 5 ++++
arch/x86/kernel/tdx.c | 61 ++++++++++++++++++++++++++++++++++----
2 files changed, 60 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index 90eb61b07d1f..b98de067257b 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -14,9 +14,14 @@
*/
#define TDCALL ".byte 0x66,0x0f,0x01,0xcc"

+#define TDVMCALL 0
#define TDINFO 1
#define TDGETVEINFO 3

+/* TDVMCALL R10 Input */
+#define TDVMCALL_STANDARD 0
+#define TDVMCALL_VENDOR 1
+
/* Common API to check TDX support in decompression and common kernel code. */
bool is_tdx_guest(void);

diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
index ae2d5c847700..25dd33bc2e49 100644
--- a/arch/x86/kernel/tdx.c
+++ b/arch/x86/kernel/tdx.c
@@ -51,6 +51,45 @@ static void tdx_get_info(void)
td_info.attributes = rdx;
}

+static __cpuidle void tdx_halt(void)
+{
+ register long r10 asm("r10") = TDVMCALL_STANDARD;
+ register long r11 asm("r11") = EXIT_REASON_HLT;
+ register long rcx asm("rcx");
+ long ret;
+
+ /* Allow to pass R10 and R11 down to the VMM */
+ rcx = BIT(10) | BIT(11);
+
+ asm volatile(TDCALL
+ : "=a"(ret), "=r"(r10), "=r"(r11)
+ : "a"(TDVMCALL), "r"(rcx), "r"(r10), "r"(r11)
+ : );
+
+ /* It should never fail */
+ BUG_ON(ret || r10);
+}
+
+static __cpuidle void tdx_safe_halt(void)
+{
+ register long r10 asm("r10") = TDVMCALL_STANDARD;
+ register long r11 asm("r11") = EXIT_REASON_HLT;
+ register long rcx asm("rcx");
+ long ret;
+
+ /* Allow to pass R10 and R11 down to the VMM */
+ rcx = BIT(10) | BIT(11);
+
+ /* Enable interrupts next to the TDVMCALL to avoid performance degradation */
+ asm volatile("sti\n\t" TDCALL
+ : "=a"(ret), "=r"(r10), "=r"(r11)
+ : "a"(TDVMCALL), "r"(rcx), "r"(r10), "r"(r11)
+ : );
+
+ /* It should never fail */
+ BUG_ON(ret || r10);
+}
+
void __init tdx_early_init(void)
{
if (!cpuid_has_tdx_guest())
@@ -60,6 +99,9 @@ void __init tdx_early_init(void)

tdx_get_info();

+ pv_ops.irq.safe_halt = tdx_safe_halt;
+ pv_ops.irq.halt = tdx_halt;
+
pr_info("TDX guest is initialized\n");
}

@@ -86,10 +128,17 @@ unsigned long tdx_get_ve_info(struct ve_info *ve)
int tdx_handle_virtualization_exception(struct pt_regs *regs,
struct ve_info *ve)
{
- /*
- * TODO: Add handler support for various #VE exit
- * reasons
- */
- pr_warn("Unexpected #VE: %d\n", ve->exit_reason);
- return -EFAULT;
+ switch (ve->exit_reason) {
+ case EXIT_REASON_HLT:
+ tdx_halt();
+ break;
+ default:
+ pr_warn("Unexpected #VE: %d\n", ve->exit_reason);
+ return -EFAULT;
+ }
+
+ /* After successful #VE handling, move the IP */
+ regs->ip += ve->instr_len;
+
+ return ret;
}
--
2.25.1
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