> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:vkuzn...@redhat.com]
> Sent: Friday, April 7, 2017 4:27 AM
> To: de...@linuxdriverproject.org; x...@kernel.org
> Cc: linux-ker...@vger.kernel.org; KY Srinivasan <k...@microsoft.com>;
> Haiyang Zhang <haiya...@microsoft.com>; Stephen Hemminger
> <sthem...@microsoft.com>; Thomas Gleixner <t...@linutronix.de>; Ingo
> Molnar <mi...@redhat.com>; H. Peter Anvin <h...@zytor.com>; Steven
> Rostedt <rost...@goodmis.org>; Jork Loeser <jork.loe...@microsoft.com>
> Subject: [PATCH 2/7] x86/hyper-v: fast hypercall implementation
>
> 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 <vkuzn...@redhat.com>
> ---
> arch/x86/include/asm/mshyperv.h | 37
> +++++++++++++++++++++++++++++++++++++
> arch/x86/include/uapi/asm/hyperv.h | 19 +++++++++++++++++++
> 2 files changed, 56 insertions(+)
>
> diff --git a/arch/x86/include/asm/mshyperv.h
> b/arch/x86/include/asm/mshyperv.h
> index 331e834..9a5f58b 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -216,6 +216,43 @@ 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};
Defining the hyper-call arguments on the stack can be problematic
if CONFIG_VMAP_STACK is defined - since we are passing the guest
physical address to the hypervisor, we cannot have the arguments
straddle a page boundary.
We have dealt with this issue currently by making sure the arguments are
never on the stack via different means. Perhaps, we can allocate memory
on a per-cpu basis that can be used for this purpose. In fact, this is what I
have done
for the hv_post_message hypercall. We can just rename that page and use it in
all
hypercalls - we can just allocate two pages on a per-CPU basis for this purpose
(for input and output parameters).
> +
> + 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;
> +
> + __asm__ __volatile__ ("call *%6"
> + : "=d"(hv_status_hi),
> + "=a"(hv_status_lo) :
> + "d" (control.as_uint32_hi),
> + "a" (control.as_uint32_lo),
> + "c" ((u32)input1),
> + "b" ((u32)(input1 >> 32)),
> + "m" (hv_hypercall_pg)
> + : "cc");
> +
> + 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
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