[PATCH v2 04/10] x86/hyper-v: fast hypercall implementation

[Vitaly Kuznetsov]

Hyper-V supports 'fast' hypercalls when all parameters are passed through
registers. Implement an inline version of a simpliest of these calls:
hypercall with one 8-byte input and no output.

Proper hypercall input interface (struct hv_hypercall_input) definition is
added as well.

Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
Changes since v1:
- rcx/rdx on x86_64 and ecx on x86 are now specified with '+' as hypervisor
  is allowed to write there, clobber esi/edi on x86 [Jork Loeser].
- Had to introduce input1_hi/input1_lo to make gcc happy as specifying '+'
  for something like 'input1>>32' doesn't work.
---
 arch/x86/include/asm/mshyperv.h    | 39 ++++++++++++++++++++++++++++++++++++++
 arch/x86/include/uapi/asm/hyperv.h | 19 +++++++++++++++++++
 2 files changed, 58 insertions(+)

diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index a9c6c10..7b9b404 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -216,6 +216,45 @@ static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
 #endif /* !x86_64 */
 }
 
+/* Fast hypercall with 8 bytes of input and no output */
+static inline u64 hv_do_fast_hypercall8(u16 code, u64 input1)
+{
+	union hv_hypercall_input control = {0};
+
+	control.code = code;
+	control.fast = 1;
+#ifdef CONFIG_X86_64
+	{
+		u64 hv_status;
+
+		__asm__ __volatile__("call *%3"
+				     : "=a" (hv_status),
+				       "+c" (control.as_uint64), "+d" (input1)
+				     : "m" (hv_hypercall_pg)
+				     : "cc", "r8", "r9", "r10", "r11");
+		return hv_status;
+	}
+#else
+	{
+		u32 hv_status_hi, hv_status_lo;
+		u32 input1_hi = (u32)(input1 >> 32);
+		u32 input1_lo = (u32)input1;
+
+		__asm__ __volatile__ ("call *%6"
+				      : "=d"(hv_status_hi),
+					"=a"(hv_status_lo),
+					"+c"(input1_lo)
+				      :	"d" (control.as_uint32_hi),
+					"a" (control.as_uint32_lo),
+					"b" (input1_hi),
+					"m" (hv_hypercall_pg)
+				      : "cc", "edi", "esi");
+
+		return hv_status_lo | ((u64)hv_status_hi << 32);
+	}
+#endif
+}
+
 void hyperv_init(void);
 void hyperv_report_panic(struct pt_regs *regs);
 bool hv_is_hypercall_page_setup(void);
diff --git a/arch/x86/include/uapi/asm/hyperv.h b/arch/x86/include/uapi/asm/hyperv.h
index 432df4b..c87e900 100644
--- a/arch/x86/include/uapi/asm/hyperv.h
+++ b/arch/x86/include/uapi/asm/hyperv.h
@@ -256,6 +256,25 @@
 #define HV_PROCESSOR_POWER_STATE_C2		2
 #define HV_PROCESSOR_POWER_STATE_C3		3
 
+/* Hypercall interface */
+union hv_hypercall_input {
+	u64 as_uint64;
+	struct {
+		__u32 as_uint32_lo;
+		__u32 as_uint32_hi;
+	};
+	struct {
+		__u64 code:16;
+		__u64 fast:1;
+		__u64 varhead_size:10;
+		__u64 reserved1:5;
+		__u64 rep_count:12;
+		__u64 reserved2:4;
+		__u64 rep_start:12;
+		__u64 reserved3:4;
+	};
+};
+
 /* hypercall status code */
 #define HV_STATUS_SUCCESS			0
 #define HV_STATUS_INVALID_HYPERCALL_CODE	2
-- 
2.9.3