From mboxrd@z Thu Jan  1 00:00:00 1970
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [v3 PATCH 07/10] x86: Add emulation code for UMIP instructions
Date: Wed, 25 Jan 2017 12:38:55 -0800
Message-ID: <145900b0-b386-e32c-cd79-cf7c47c14616@zytor.com>
References: <20170125202353.101059-1-ricardo.neri-calderon@linux.intel.com>
 <20170125202353.101059-8-ricardo.neri-calderon@linux.intel.com>
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <20170125202353.101059-8-ricardo.neri-calderon@linux.intel.com>
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-msdos.vger.kernel.org>
Content-Type: text/plain; charset="us-ascii"
To: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>, Ingo Molnar <mingo@redhat.com>, Thomas Gleixner <tglx@linutronix.de>, Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>, Andrew Morton <akpm@linux-foundation.org>, Brian Gerst <brgerst@gmail.com>, Chris Metcalf <cmetcalf@mellanox.com>, Dave Hansen <dave.hansen@linux.intel.com>, Paolo Bonzini <pbonzini@redhat.com>, Liang Z Li <liang.z.li@intel.com>, Masami Hiramatsu <mhiramat@kernel.org>, Huang Rui <ray.huang@amd.com>, Jiri Slaby <jslaby@suse.cz>, Jonathan Corbet <corbet@lwn.net>, "Michael S. Tsirkin" <mst@redhat.com>, Paul Gortmaker <paul.gortmaker@windriver.com>, Vlastimil Babka <vbabka@suse.cz>, Chen Yucong <slaoub@gmail.com>, Alexandre Julliard <julliard@winehq.org>, Fenghua Yu <fenghua.yu@intel.com>, Stas Sergeev <stsp@list.ru>, "Ravi V. Shankar" <ravi.v.shankar@intel.com>, Shuah Khan <shuah@kernel.org>, linux-kernel@vger.kern

On 01/25/17 12:23, Ricardo Neri wrote:
> +	case UMIP_SMSW:
> +		dummy_value = CR0_STATE;

Unless the user space process is running in 64-bit mode this value
should be & 0xffff.  I'm not sure if we should even support fixing up
UMIP instructions in 64-bit mode.

Also, please put an explicit /* fall through */ here.

> +	/*
> +	 * These two instructions return a 16-bit value. We return
> +	 * all zeros. This is equivalent to a null descriptor for
> +	 * str and sldt.
> +	 */
> +	case UMIP_SLDT:
> +	case UMIP_STR:
> +		/* if operand is a register, it is zero-extended*/
> +		if (X86_MODRM_MOD(insn->modrm.value) == 3) {
> +			memset(data, 0, insn->opnd_bytes);
> +			*data_size = insn->opnd_bytes;
> +		/* if not, only the two least significant bytes are copied */
> +		} else {
> +			*data_size = 2;
> +		}
> +		memcpy(data, &dummy_value, sizeof(dummy_value));
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +	return 0;


> +bool fixup_umip_exception(struct pt_regs *regs)
> +{
> +	struct insn insn;
> +	unsigned char buf[MAX_INSN_SIZE];
> +	/* 10 bytes is the maximum size of the result of UMIP instructions */
> +	unsigned char dummy_data[10] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
> +#ifdef CONFIG_X86_64
> +	int x86_64 = user_64bit_mode(regs);
> +#else
> +	int x86_64 = 0;
> +#endif

Again, could we simply do:

	if (user_64bit_mode(regs))
		return false;

or are there known users of these instructions *in 64-bit mode*?

	-hpa