Re: The virtuailization patches break Voyager.

[Jeremy Fitzhardinge <jeremy@goop.org>]

Eric W. Biederman wrote:
> Guys currently I am horrified by the ease at which I can find
> bugs in the pending paravirtualization patches.  I have barely
> even looked at arch/i386 in the -mm tree and it feels like
> I am tripping over significant bugs left and right.
>   

Well, I appreciate any and all review comments you have to make.

> Because no one has heeded my advice and put in a proper platform
> layer on arch/i386 and we are instead doing a half baked job
> with paravirt_ops it is still trivially easy to miss the
> fact that subarchitectures do something different, and thus
> it is easy to miss when you break a sub architecture on
> arch/i386.
>   

Yes. Though in many ways paravirt_ops is approaching that platform
layer. In the next round of work, it might be worth renaming it and
actually using it to subsume the subarch mechanism into something that
can deal with any architecture at runtime. While this hasn't been an
explicit goal of the current round of work, I've tried to point things
in that direction where I can (smp_ops and reboot_ops being specific
examples of that).

But you're right; we've been fairly cavalier about Voyager in
particular, with the hope that James' machine will die before he notices
we've broken the build. (Or perhaps it has, and he just keeps building
voyager kernels to torment us.)

> Not that the paravirtuailzation patches are even safe on the
> primary arch/i386.
>   

Are you referring to the PSE pagetable setup problem we've been
discussing, or do you have something else in mind?

> To some extent I grant with major changes a little goofing up on
> pending patches is to be expected, but it would be nice if
> things were restructured to make it harder to miss the
> subarchitectures on arch/i386.
>
> The patch known as x86_64-mm-use-per-cpu-gdt-immediately-upon-boot
> on -mm currently breaks voyager smp support in some very obvious ways.
>
> Making init_gdt a function which is called from voyager_smp.c static
> in smpboot.c a file that is not even used on voayger is an obvious
> one.
>
> Adding start_pda and not setting it in voyager_smp is another.
>
> Rusty do you think you can address this?

Well, it will probably need to be done after the following patches which
get rid of the PDA altogether. But the boot-time setup is now pretty
simple, so it should just be a matter of putting a couple of init_gdts
in the right places. (It is non-static now too.)

J