http://people.cs.pitt.edu/~anz28/papers/2013_kitten_gdb_tr.pdf
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What is a Hypercall?
Hypercall is an explicit call from Virtual Machine (VM) into the underlying VM Moniter (VMM). That is, a hypercall issued from the guest will cause a VM exit from the guest into the VMM. In this sense, it is kinda like syscall, which will result in a trap from userspace into kernel space. Thus, hypercall can serve as a communication approach between the guest and the underlying VMM. The guest can issue hypercalls via VMMCALL instruction on AMD SVM machine or VMCALL on Intel VMX machine.
Adding a Hypercall in Palacios
Palacios maintains a global hypercall map, which maintains the mapping between the unique hypercall number and the hypercall handler. (Each hypercall is associated with a unique hypercall number.). Therefore, to add a hypercal in Palacios, you need to:
- Implement a handler for the hypercall.
- Assign a unique hypercall number for the hypercall.
- Register the hypercall handler and the hypercall number with Palacios.
Sample Example:
unsigned long param1 = *(unsigned long *) &info->vm_regs.rbx;
unsigned long param2 = *(unsigned long *) &info->vm_regs.rcx;
unsigned long param3 = *(unsigned long *) &info->vm_regs.rdx;
V3_Print("param1=%lu param2=%lu param3=%lu\n", param1, parma2, param3);
info->vm_regs.rax = 0; //return value of the hypercall
}
v3_register_hypercall(vm, HCALL_EXAMPLE_ID, handle_hcall, NULL);
Note: The hypercall management APIs in Palacios are contained in palacios/include/palacios/vmm_hypercall.h and palacios/src/palacios/vmm_hypercall.c.
Issuing Hypercalls from Palacios Guest
“Up to four arguments may be passed in rbx, rcx, rdx, and rsi respectively. The hypercall number should be placed in rax and the return value will be placed in rax. No other registers will be clobbered unless explicitly stated by the particular hypercall.” (quoted from [1])
For exmaple, on a AMD SVM machine, a hypercall with 3 parameters can be issued via the following code:
int hcall3(unsigned long hcall_id, unsigned long param1, unsigned long param2, unsigned long param3){
int ret;
__asm__ volatile(
VMMCALL
: “=a”(ret)
: “a”(hcall_id), “b”(param1), “c”(param2), “d”(param3)
);
return ret;
}
References:
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perf: linux鍐呮牳abi: http://web.eece.maine.edu/~vweaver/projects/perf_events/perf_event_open.html
perf: perf stat鐨勪竴涓柊鏇懼弬鏁版敮鎸佸懆鏈熸х殑鎵撳嵃鍑篶ounter鍐呭: https://patchwork.kernel.org/patch/2004891/
鏈夊叧performance hardware counter鐨勮櫄鎷熷寲: http://web.eece.maine.edu/~vweaver/projects/perf_events/virtualization.html
鍙︿竴涓湁鍏硃erformance profiling鐨勫父鐢ㄥ伐鍏?PAPI: http://icl.cs.utk.edu/projects/papi/wiki/Main_Page
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