linux-kernel - Re: [PATCH v3 04/10] x86/hyper-v: fast hypercall implementation

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Date:   Mon, 22 May 2017 12:44:02 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     devel@...uxdriverproject.org,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Jork Loeser <Jork.Loeser@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v3 04/10] x86/hyper-v: fast hypercall implementation

Andy Lutomirski <luto@...nel.org> writes:

> On 05/19/2017 07:09 AM, Vitaly Kuznetsov wrote:
>> 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@...hat.com>
>> Acked-by: K. Y. Srinivasan <kys@...rosoft.com>
>> Tested-by: Simon Xiao <sixiao@...rosoft.com>
>> Tested-by: Srikanth Myakam <v-srm@...rosoft.com>
>> ---
>>   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 e293937..028e29b 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
>
> This is going to need an explicit "sp" annotation to force a stack
> frame, I think.  Otherwise objtool is likely to get mad in a
> frame-pointer-omitted build.
>

You mean I should do something like 

diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 359967f..f86c4ae 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -221,6 +221,7 @@ static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
 static inline u64 hv_do_fast_hypercall8(u16 code, u64 input1)
 {
        union hv_hypercall_input control = {0};
+       register void *__sp asm(_ASM_SP);
 
        control.code = code;
        control.fast = 1;
@@ -228,8 +229,8 @@ static inline u64 hv_do_fast_hypercall8(u16 code, u64 input1)
        {
                u64 hv_status;
 
-               __asm__ __volatile__("call *%3"
-                                    : "=a" (hv_status),
+               __asm__ __volatile__("call *%4"
+                                    : "=a" (hv_status), "+r" (__sp),
                                       "+c" (control.as_uint64), "+d" (input1)
                                     : "m" (hv_hypercall_pg)
                                     : "cc", "r8", "r9", "r10", "r11");
@@ -241,10 +242,11 @@ static inline u64 hv_do_fast_hypercall8(u16 code, u64 input1)
                u32 input1_hi = (u32)(input1 >> 32);
                u32 input1_lo = (u32)input1;
 
-               __asm__ __volatile__ ("call *%6"
+               __asm__ __volatile__ ("call *%7"
                                      : "=d"(hv_status_hi),
                                        "=a"(hv_status_lo),
-                                       "+c"(input1_lo)
+                                       "+c"(input1_lo),
+                                       "+r"(__sp)
                                      : "d" (control.as_uint32_hi),
                                        "a" (control.as_uint32_lo),
                                        "b" (input1_hi),

(stollen from 0e8e2238)? hv_do_hypercall() will need this adjustment
too, I think.

-- 
  Vitaly