Re: [PATCH v2] x86/vpci: fix handling of BAR overlaps with non-hole regions

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, May 21, 2025 at 04:31:33PM +0200, Jan Beulich wrote:
> On 21.05.2025 13:34, Roger Pau Monné wrote:
> > On Wed, May 21, 2025 at 10:29:26AM +0200, Jan Beulich wrote:
> >> On 16.05.2025 10:31, Roger Pau Monne wrote:
> >>> For once the message printed when a BAR overlaps with a non-hole regions 
> >>> is
> >>> not accurate on x86.  While the BAR won't be mapped by the vPCI logic, it
> >>> is quite likely overlapping with a reserved region in the memory map, and
> >>> already mapped as by default all reserved regions are identity mapped in
> >>> the p2m.  Fix the message so it just warns about the overlap, without
> >>> mentioning that the BAR won't be mapped, as this has caused confusion in
> >>> the past.
> >>
> >> I was trying to get back to this, but my attempt to use this "fixed
> >> message" as an anchor failed: You don't modify any existing message, and
> >> hence I was unable to determine which other message you refer to here.
> >> None of the ones I looked at appear to fit this description.
> > 
> > OK, it's a bit tricky.  Note how the new implementation of
> > pci_check_bar() unconditionally returns true, which means the message
> > in modify_bars() will never be printed on x86.  Instead a slightly
> > different warning message is printed in the x86 implementation of
> > pci_check_bar().
> > 
> > That's what the above paragraph attempts to explain.
> > 
> > Maybe I need to adjust the last sentence so it's:
> > 
> > "Avoiding printing the warning message in modify_bars(), and instead
> > print a more lax message in the x86 implementation of pci_check_bar()
> > to note the current BAR position overlaps with non-hole region(s)."
> > 
> > Does the above make it a bit clearer?
> 
> Yes, it definitely does. And with use of that I'm now also feeling reasonably
> confident to offer
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Thanks, sorry this was a bit dense.

Roger.