Re: [PATCH v5 04/17] x86/acrn: Introduce hypercall interfaces
From: Shuo A Liu
Date: Tue Oct 20 2020 - 21:16:16 EST
On Tue 20.Oct'20 at 10:16:02 -0400, Arvind Sankar wrote:
On Tue, Oct 20, 2020 at 10:30:17AM +0800, Shuo A Liu wrote:
On Mon 19.Oct'20 at 22:08:51 -0400, Arvind Sankar wrote:
>On Tue, Oct 20, 2020 at 09:38:09AM +0800, Shuo A Liu wrote:
>> On Mon 19.Oct'20 at 18:15:15 -0400, Arvind Sankar wrote:
>> >On Mon, Oct 19, 2020 at 02:17:50PM +0800, shuo.a.liu@xxxxxxxxx wrote:
>> >> From: Shuo Liu <shuo.a.liu@xxxxxxxxx>
>> >>
>> >> The Service VM communicates with the hypervisor via conventional
>> >> hypercalls. VMCALL instruction is used to make the hypercalls.
>> >>
>> >> ACRN hypercall ABI:
>> >> * Hypercall number is in R8 register.
>> >> * Up to 2 parameters are in RDI and RSI registers.
>> >> * Return value is in RAX register.
>> >>
>> >> Introduce the ACRN hypercall interfaces. Because GCC doesn't support R8
>> >> register as direct register constraints, use supported constraint as
>> >> input with a explicit MOV to R8 in beginning of asm.
>> >>
>> >> +static inline long acrn_hypercall0(unsigned long hcall_id)
>> >> +{
>> >> + long result;
>> >> +
>> >> + asm volatile("movl %1, %%r8d\n\t"
>> >> + "vmcall\n\t"
>> >> + : "=a" (result)
>> >> + : "ir" (hcall_id)
>> >
>> >Is the hypercall id an unsigned long (64 bits) or an unsigned int (32
>> >bits)? This will generate broken assembly if the "r" option is chosen,
>> >eg something like
>> > movl %rdi, %r8d
>>
>> Yes, it can be an unsigned long. So do MOV explicitly.
>>
>> asm volatile("movq %1, %%r8\n\t"
>> "vmcall\n\t"
>> : "=a" (result)
>> : "ir" (hcall_id)
>>
>> Thanks
>
>All the hypercall ID's defined seem to be only 32 bits though?
Yes, they are.
The paramter is unsigned long, use movq to align it.
I don't understand what you mean by alignment here, but I was asking why
hcall_id is unsigned long and not unsigned int (or u32) if you only need
32 bits?
The hypervisor is using R8 as the input of hcall_id. So i just want to
keep it consistent.