Re: [RFC PATCH v2 3/3] arch/x86/acrn: add hypercall for acrn_guest

From: Zhao, Yakui
Date: Sun Apr 07 2019 - 23:36:28 EST

On 2019å04æ06æ 03:19, Thomas Gleixner wrote:
On Tue, 26 Mar 2019, Zhao Yakui wrote:

When acrn_hypervisor is detected, the hypercall is needed so that the
acrn guest can query/config some settings. For example: it can be used
to query the resources in hypervisor and manage the CPU/memory/device/
interrupt for Guest system.

So the hypercall is added so that the kernel can communicate with the
low-level acrn-hypervisor. On x86 it is implemented by using vmacll when

is implemented with the VMCALL instruction

the acrn hypervisor is enabled.

+++ b/arch/x86/include/asm/acrn_hypercall.h
@@ -0,0 +1,84 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+ * acrn_hypercall.h : acrn hypervisor call API

No file names in headers please. They are pointless and get out of sync
when files are renamed.

Sure. It will be removed in next vesion.

+ */
+#ifndef __ACRN_HYPERCALL_H__
+#define __ACRN_HYPERCALL_H__

asm headers start with


This will be fixed.

+#include <linux/errno.h>
+ * Hypercalls for ACRN Guest
+ *
+ * Hypercall number is passed in r8 register.
+ * Return value will be placed in rax.
+ * Up to 2 arguments are passed in rdi, rsi.
+ */
+static inline long acrn_hypercall0(unsigned long hcall_id)

Remove the empty new line please.

+ register long result asm("rax");
+ register unsigned long r8 asm("r8") = hcall_id;

Please order them the other way around, like a reverse christmas tree:

register unsigned long r8 asm("r8") = hcall_id;
register long result asm("rax");

That's way simpler to read.

This will be fixed.

+ asm volatile(".byte 0x0F,0x01,0xC1\n"
+ : "=r"(result)
+ : "r"(r8));

Please mention in the changelog why this is implemented with bytes and not
with the proper mnemonic. I assume it depends on binutils, so please
document which version of binutils supports the mnemonic.

I check the binutils version mentioned in Document/changes.
(binutils, 2.20)
It seems that the "vmcall" is already supported.
So the "vmcall" mnemonic will be used to make it readable.

And in the first function, i.e. hypercall0, add a comment above the asm
volatile() to that effect as well.