Re: [PATCH][4.15] x86/shadow: replace bogus return path in shadow_get_page_from_l1e()

[Ian Jackson <iwj@xxxxxxxxxxxxxx>]

Jan Beulich writes ("Re: [PATCH][4.15] x86/shadow: replace bogus return path in 
shadow_get_page_from_l1e()"):
> On 26.02.2021 16:08, Jan Beulich wrote:
> > Prior to be640b1800bb ("x86: make get_page_from_l1e() return a proper
> > error code") a positive return value did indicate an error. Said commit
> > failed to adjust this return path, but luckily the only caller has
> > always been inside a shadow_mode_refcounts() conditional.
> > 
> > Subsequent changes caused 1 to end up at the default (error) label in
> > the caller's switch() again, but the returning of 1 (== _PAGE_PRESENT)
> > is still rather confusing here, and a latent risk.
> 
> The confusion on my part was so significant that I screwed up
> the shadow mode fix for "VMX: use a single, global APIC access
> page" (which turned out to be necessary) initially. Hence my
> proposing this for 4.15.

Right.  I'm sympathetic, but I would like to hear from another
maintainer of this code, as to their opinion about how much this
change removes the potential for confusion.

>  I'm on the edge at this point whether
> I'd even consider this a backporting candidate.

I think you mean you think that even though the code does not compile
to something actually buggy now, this is sufficiently bad a confusion
that it risks bugs in stable trees, so you are considering
backporting.

Thanks, that is a useful piece of perspective.

Ian.