linux-kernel - Re: [PATCH 1/6] x86: Add VMWare Host Communication Macros

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Date:	Tue, 1 Dec 2015 14:49:11 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Sinclair Yeh <syeh@...are.com>, x86@...nel.org
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Alok Kataria <akataria@...are.com>,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Xavier Deguillard <xdeguillard@...are.com>
Subject: Re: [PATCH 1/6] x86: Add VMWare Host Communication Macros

On 12/01/15 14:18, Sinclair Yeh wrote:
> These macros will be used by multiple VMWare modules for handling
> host communication.

> +	__asm__ __volatile__ ("inl %%dx" :                              \

This is odd at best; the standard assembly form of this instruction is:

	inl (%dx),%eax

Also, we don't need the underscored forms of asm and volatile for kernel
code.

> +	__asm__ __volatile__ ("movq %13, %%rbp;"        \
> +		"cld; rep outsb; "                      \
> +		"movq %%rbp, %6" :                      \

cld shouldn't be necessary here, DF=0 is part of the normal ABI environment.

You also don't save/restore %rbp here, but you do below?  Seems very odd.

It might be better do so something like:

+#define VMW_PORT_HB_OUT(in1, in2, port_num, magic,     \
+			eax, ebx, ecx, edx, si, di, bp) \
+({                                                     \
+	__asm__ __volatile__ ("xchgq %6, %%rbp;"        \
+		"cld; rep outsb; "                      \
+		"xchgq %%rbp, %6" :                     \
+		"=a"(eax),                              \
+		"=b"(ebx),                              \
+		"=c"(ecx),                              \
+		"=d"(edx),                              \
+		"+S"(si),                               \
+		"+D"(di),                               \
+		"+r"(bp) :                              \
+		"a"(magic),                             \
+		"b"(in1),                               \
+		"c"(in2),                               \
+		"d"(port_num) :                         \
+		"memory", "cc");                        \
+})



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