Hi,

On Sat, Jun 21, 2025 at 10:43:23PM -0700, Mike Larkin wrote:
> ...
> I think this locore diff below looks ok to me but it changes some very
> fundamental early boot behavior. I was asking before what your plan is for
> testing this before commit. I don't think testing this on just a handful
> of machines is sufficient. It's particularly tough with this one as if it
> breaks someone, the machine will pretty much be bricked and require fixing
> via install media. That's why I'm hesitant.
> 
> If you are ready to handle any fallout, then sure. It's probably the right
> time in the release process for this. ok mlarkin on the diff itself in that
> case. There are a few things we can change later (like using .Lxxx in all
> symbols in locore0 and there are a few style(9) things) but nothing that
> warrants fixing now.
> 
> P.S. hshoexer: The locore0 page gets unmapped right after we are done with it;
> can you please verify that the #VC traps and locore0 IDTs aren't needed after
> that unmapping?

yes, the locore0 #VC trap handler will not be needed after we are reach
init_x86_64().  The next diffs will deal with this:  init_x86_64()
will setups a temporary "early" IDT right away to deal with #VC during
bootstrap.  And when init_x86_64() sets up the actual IDT an entry for
#VC is included.

Fwiw:  I have some experimental proof-of-concept code, that uses
paravirtualisation to completely avoid #VC as soon as the kernel is up
and running (and SEV-ES/SNP is enabled).

Take care,
Hans-Joerg

• smime.p7s (5K)