Re: [PATCH v3] xen/x86/pvh: handle ACPI RSDT table in PVH Dom0 build

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

On Thu, Apr 25, 2024 at 09:26:59AM +0200, Jan Beulich wrote:
> On 25.04.2024 09:10, Roger Pau Monné wrote:
> > On Thu, Apr 25, 2024 at 08:12:09AM +0200, Jan Beulich wrote:
> >> On 24.04.2024 21:18, Daniel P. Smith wrote:
> >>> @@ -1089,6 +1098,9 @@ static int __init pvh_setup_acpi_xsdt(struct domain 
> >>> *d, paddr_t madt_addr,
> >>>      xsdt->header = *table;
> >>>      acpi_os_unmap_memory(table, sizeof(*table));
> >>>  
> >>> +    /* In case the header is an RSDT copy, blindly ensure it has an XSDT 
> >>> sig */
> >>> +    xsdt->header.signature[0] = 'X';
> >>
> >> This is in no way "blindly". The size of the table elements being different
> >> between RSDT and XSDT makes it mandatory to have the correct signature. 
> >> Else
> >> the consumer of the struct is going to be misled.
> > 
> > The "blindly" IMO refers to the fact that the table might already have
> > the right signature, but this is not checked, IOW we could do:
> > 
> > if ( xsdt->header.signature[0] == 'R' )
> >     xsdt->header.signature[0] = 'X';
> 
> Right, and indeed I was seeing this as a possible further interpretation.
> Yet given multiple ways of reading this, I'm of the opinion that it wants
> adjusting. ", ... unconditionally ensure it has ... " may already do.
> Simply dropping "blindly" would too be okay with me.

FWIW, I'm fine with any of the proposed adjustments.

Thanks, Roger.