From: "Sinclair Yeh" <syeh@vmware.com>
Date: Fri, 4 Dec 2015 14:33:08 -0800
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Alok Kataria <akataria@vmware.com>,
        linux-kernel@vger.kernel.org,
        virtualization@lists.linux-foundation.org,
        Xavier Deguillard <xdeguillard@vmware.com>
Subject: Re: [PATCH 1/6] x86: Add VMWare Host Communication Macros
Message-ID: <20151204223308.GA28421@syeh-linux>
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 <565E23E7.5090800@zytor.com>
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Thanks Peter.


On Tue, Dec 01, 2015 at 02:49:11PM -0800, H. Peter Anvin wrote:
> 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

Ok, I'm not sure why this worked and compiled before.  Fixed.

> 
> 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.

Good catch.  Fixed.

> 
> 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");                        \
> +})

This is great.  Changed.

Updated patch set incoming.

Sinclair

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