Re: [Xen-devel] [PATCH v2 1/4] x86/microcode: Improve documentation and parsing for ucode=

[Eslam Elnikety <elnikety@xxxxxxxxxx>]

On 20.01.20 09:42, Jan Beulich wrote:
> On 17.01.2020 20:06, Eslam Elnikety wrote:
> > On 20.12.19 10:53, Jan Beulich wrote:
> > > On 19.12.2019 22:08, Eslam Elnikety wrote:
> > > > On 18.12.19 12:49, Jan Beulich wrote:
> > > > > On 18.12.2019 02:32, Eslam Elnikety wrote:
> > > > > > Decouple the microcode referencing mechanism when using GRUB to that
> > > > > > when using EFI. This allows us to avoid the "unspecified effect" of
> > > > > > using `<integer> | scan` along xen.efi.
> > > > > I guess "unspecified effect" in the doc was pretty pointless - such
> > > > > options have been ignored before; in fact ...
> > > > >
> > > > > > With that, Xen can explicitly
> > > > > > ignore those named options when using EFI.
> > > > > ... I don't see things becoming any more explicit (not even parsing
> > > > > the options was quite explicit to me).
> > > > I agree that those options have been ignored so far in the case of EFI.
> > > > The documentation contradicts that however. The documentation:
> > > > * says <integer> has unspecified effect.
> > > > * does not mention anything about scan being ignored.
> > > >
> > > > With this patch, it is explicit in code and in documentation that both
> > > > options are ignored in case of EFI.
> > > But isn't it rather that ucode=scan could (and hence perhaps should)
> > > also have its value on EFI?
> > I do not see "ucode=scan" applicable in anyway in the case of EFI. In
> > EFI, there are not "modules" to scan through, but rather the efi config
> > points exactly to the microcode blob.
> What would be wrong with the EFI code to also inspect whatever has been
> specified with ramdisk= if there was no ucode= ?
>
> Jan
I see, interesting. This sounds like a legitimate use case indeed. I 
wonder, would I be breaking anything if I simply allow the existing code 
that iterates over modules to kick in when ucode=scan irrespective of 
EFI or legacy boot? Also, it seems to me that the ucode= specified by 
efi.cfg would take precedence over the ucode=scan. Do not you think?
Eslam

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