KY Srinivasan <k...@microsoft.com> writes:
>> -----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).
This is fast hypercall and not the normal one - we pass control to
register so we're fine here (and I'd actually expect the compiler to put
it to the propper register in the first place.
>> +
>> + 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
--
Vitaly
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