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From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Wei Liu <wei.liu2@citrix.com>, Jan Beulich <JBeulich@suse.com>
Cc: Xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH RFC 2/2] xen: make available hvm_fep to non-debug build as well
Date: Thu, 16 Jun 2016 13:12:34 +0100	[thread overview]
Message-ID: <f7719257-0808-5189-49b4-220477d373cc@citrix.com> (raw)
In-Reply-To: <20160616115209.GP28116@citrix.com>

On 16/06/16 12:52, Wei Liu wrote:
>
>>> +        printk("**********************************************\n");
>>> +        printk("******* WARNING: HVM FORCED EMULATION PREFIX IS PERMITTED\n");

I would say "available" rather than permitted in this case.

>>> +        printk("******* This option is *ONLY* intended to aid debugging "
>>> +               "and testing of Xen\n");

Despite the line length, I would keep this string on a single line.  If
you want it a little shorter, you can drop "debugging and", leaving just
testing.

>>> +        printk("******* that HVM guest can enter instruction emulator "
>>> +               "with UD instruction.\n");

I think this like isn't necessary.  Anyone who is unclear what FEP is
can look it up.

>>> +        printk("******* It has implication on the security of the system.\n");

implications.

>>> +        printk("******* Please *DO NOT* use this in production.\n");
>>> +        printk("**********************************************\n");
>>> +        add_taint(TAINT_HVM_FEP);
>> Should we perhaps taint the system only the first time a guest
>> makes use of this?
>>
> Doesn't that add overhead to a potential hot path? Arguably it is only
> setting a bit in a flag, but still...

FEP is not a fastpath at all.  It would be fine to defer to
hvm_ud_intercept().

~Andrew

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  reply	other threads:[~2016-06-16 12:12 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-15 14:31 [PATCH RFC 0/2] Make hvm_fep available to non-debug builds Wei Liu
2016-06-15 14:31 ` [PATCH RFC 1/2] xen/kernel: document 'C' in print_tainted Wei Liu
2016-06-15 14:53   ` Jan Beulich
2016-06-15 14:31 ` [PATCH RFC 2/2] xen: make available hvm_fep to non-debug build as well Wei Liu
2016-06-15 14:39   ` Doug Goldstein
2016-06-15 14:47     ` Wei Liu
2016-06-15 16:12       ` Doug Goldstein
2016-06-15 16:14         ` Wei Liu
2016-06-16 11:37   ` Jan Beulich
2016-06-16 11:52     ` Wei Liu
2016-06-16 12:12       ` Andrew Cooper [this message]
2016-06-16 12:20         ` Wei Liu
2016-06-16 12:31       ` Jan Beulich

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