From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: Xen-devel <xen-devel@lists.xenproject.org>,
"Wei Liu" <wl@xen.org>, "Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH 4/7] x86/ucode/intel: Reimplement get_{data, total}size() helpers
Date: Thu, 26 Mar 2020 15:09:56 +0000 [thread overview]
Message-ID: <d4b56282-1df4-0c18-9ca7-5277a3829fb3@citrix.com> (raw)
In-Reply-To: <83909134-8bd7-b1b2-40f7-040dd00cc517@suse.com>
On 26/03/2020 14:56, Jan Beulich wrote:
> On 26.03.2020 15:35, Andrew Cooper wrote:
>> On 25/03/2020 13:41, Jan Beulich wrote:
>>> On 23.03.2020 11:17, Andrew Cooper wrote:
>>>> --- a/xen/arch/x86/cpu/microcode/intel.c
>>>> +++ b/xen/arch/x86/cpu/microcode/intel.c
>>>> @@ -46,9 +46,16 @@ struct microcode_header_intel {
>>>> unsigned int sig;
>>>> unsigned int cksum;
>>>> unsigned int ldrver;
>>>> +
>>>> + /*
>>>> + * Microcode for the Pentium Pro and II had all further fields in the
>>>> + * header reserved, had a fixed datasize of 2000 and totalsize of 2048,
>>>> + * and didn't use platform flags despite the availability of the MSR.
>>>> + */
>>>> +
>>>> unsigned int pf;
>>>> - unsigned int datasize;
>>>> - unsigned int totalsize;
>>>> + unsigned int _datasize;
>>>> + unsigned int _totalsize;
>>> ... the underscores here dropped again. Or else - why did you add
>>> them? This (to me at least) doesn't e.g. make any more clear that
>>> the fields may be zero on old hardware.
>> No, but it is our normal hint that you shouldn't be using the field
>> directly, and should be using the accessors instead.
> Yet in patch 5 you do. Perhaps for an understandable reason, but
> that way you at least partly invalidate what you say above.
The net result of of patch 5 is three adjacent helpers, which are the
only code which use the fields themselves.
I can drop if you really insist. We're only talking about 400 lines or
code, or thereabouts.
>>> Furthermore - do we really need this PPro/PentiumII logic seeing
>>> that these aren't 64-bit capable CPUs?
>> I did actually drop support in one version of my series, but put it back in.
>>
>> These old microcode blobs are still around, including in some versions
>> of microcode.dat. By dropping the ability to recognise them as
>> legitimate, we'd break the logic to search through a container of
>> multiple blobs to find the one which matches.
> Oh, good point.
Shame I only came to that realisation after having reworked the series
to take it out...
I'm constructing companion document to
https://xenbits.xen.org/docs/sphinx-unstable/admin-guide/microcode-loading.html
which will live in hypervisor-guide section, and cover a whole range of
topics like this.
~Andrew
next prev parent reply other threads:[~2020-03-26 15:10 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-23 10:17 [Xen-devel] [PATCH 0/7] x86/ucode: Cleanup and fixes - Part 3/n (Intel) Andrew Cooper
2020-03-23 10:17 ` [Xen-devel] [PATCH 1/7] x86/ucode: Document the behaviour of the microcode_ops hooks Andrew Cooper
2020-03-23 12:33 ` Jan Beulich
2020-03-23 13:26 ` Andrew Cooper
2020-03-23 14:24 ` Jan Beulich
2020-03-23 10:17 ` [Xen-devel] [PATCH 2/7] x86/ucode/intel: Adjust microcode_sanity_check() to not take void * Andrew Cooper
2020-03-25 13:23 ` Jan Beulich
2020-03-23 10:17 ` [Xen-devel] [PATCH 3/7] x86/ucode/intel: Remove gratuitous memory allocations from cpu_request_microcode() Andrew Cooper
2020-03-25 13:34 ` Jan Beulich
2020-03-23 10:17 ` [Xen-devel] [PATCH 4/7] x86/ucode/intel: Reimplement get_{data, total}size() helpers Andrew Cooper
2020-03-25 13:41 ` Jan Beulich
2020-03-26 14:35 ` Andrew Cooper
2020-03-26 14:56 ` Jan Beulich
2020-03-26 15:09 ` Andrew Cooper [this message]
2020-03-26 15:19 ` Jan Beulich
2020-03-23 10:17 ` [Xen-devel] [PATCH 5/7] x86/ucode/intel: Clean up microcode_update_match() Andrew Cooper
2020-03-25 13:51 ` Jan Beulich
2020-03-26 14:36 ` Andrew Cooper
2020-03-23 10:17 ` [Xen-devel] [PATCH 6/7] x86/ucode/intel: Clean up microcode_sanity_check() Andrew Cooper
2020-03-25 14:07 ` Jan Beulich
2020-03-26 14:41 ` Andrew Cooper
2020-03-26 15:02 ` Jan Beulich
2020-03-23 10:17 ` [Xen-devel] [PATCH 7/7] x86/ucode/intel: Fold structures together Andrew Cooper
2020-03-25 14:16 ` Jan Beulich
2020-03-25 14:32 ` Andrew Cooper
2020-03-26 12:24 ` Jan Beulich
2020-03-26 14:50 ` Andrew Cooper
2020-03-26 15:05 ` Jan Beulich
2020-03-27 12:40 ` Andrew Cooper
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