Re: [PATCH v5 1/3] x86/iommu: remove regions not to be mapped

["Roger Pau Monné" <roger.pau@citrix.com>]

On Thu, Jan 25, 2024 at 01:22:15PM +0000, Andrew Cooper wrote:
> On 25/01/2024 1:13 pm, Jan Beulich wrote:
> > On 25.01.2024 13:55, Andrew Cooper wrote:
> >> On 25/01/2024 12:37 pm, Roger Pau Monné wrote:
> >>> On Thu, Jan 25, 2024 at 12:13:01PM +0100, Jan Beulich wrote:
> >>>> On 25.01.2024 09:47, Roger Pau Monné wrote:
> >>>>> On Thu, Jan 25, 2024 at 09:34:40AM +0100, Jan Beulich wrote:
> >>>>>> On 24.01.2024 18:29, Roger Pau Monne wrote:
> >>>>>>> --- a/xen/arch/x86/hvm/io.c
> >>>>>>> +++ b/xen/arch/x86/hvm/io.c
> >>>>>>> @@ -369,6 +369,22 @@ bool vpci_is_mmcfg_address(const struct domain *d, paddr_t addr)
> >>>>>>>      return vpci_mmcfg_find(d, addr);
> >>>>>>>  }
> >>>>>>>  
> >>>>>>> +int __hwdom_init vpci_subtract_mmcfg(const struct domain *d, struct rangeset *r)
> >>>>>>> +{
> >>>>>>> +    const struct hvm_mmcfg *mmcfg;
> >>>>>>> +
> >>>>>>> +    list_for_each_entry ( mmcfg, &d->arch.hvm.mmcfg_regions, next )
> >>>>>>> +    {
> >>>>>>> +        int rc = rangeset_remove_range(r, PFN_DOWN(mmcfg->addr),
> >>>>>>> +                                       PFN_DOWN(mmcfg->addr + mmcfg->size - 1));
> >>>>>> Along the lines of this, ...
> >>>>>>
> >>>>>>> --- a/xen/arch/x86/setup.c
> >>>>>>> +++ b/xen/arch/x86/setup.c
> >>>>>>> @@ -2138,6 +2138,54 @@ int __hwdom_init xen_in_range(unsigned long mfn)
> >>>>>>>      return 0;
> >>>>>>>  }
> >>>>>>>  
> >>>>>>> +int __hwdom_init remove_xen_ranges(struct rangeset *r)
> >>>>>>> +{
> >>>>>>> +    paddr_t start, end;
> >>>>>>> +    int rc;
> >>>>>>> +
> >>>>>>> +    /* S3 resume code (and other real mode trampoline code) */
> >>>>>>> +    rc = rangeset_remove_range(r, PFN_DOWN(bootsym_phys(trampoline_start)),
> >>>>>>> +                               PFN_DOWN(bootsym_phys(trampoline_end)) - 1);
> >>>>>> ... did you perhaps mean
> >>>>>>
> >>>>>>                                PFN_DOWN(bootsym_phys(trampoline_end) - 1));
> >>>>>>
> >>>>>> here (and then similarly below, except there the difference is benign I
> >>>>>> think, for the labels being page-aligned)?
> >>>>> They are all page aligned, so I didn't care much,  but now that you
> >>>>> point it might be safer to do the subtraction from the address instead
> >>>>> of the frame number, just in case.
> >>>> Hmm, no, for me neither trampoline_end nor trampoline_start are page
> >>>> aligned. While bootsym_phys(trampoline_start) is, I don't think
> >>>> bootsym_phys(trampoline_end) normally would be (it might only be by
> >>>> coincidence).
> >>> Oh, so it had been a coincidence of the build I was using I guess then.
> >> trampoline_start has to be page aligned because of constraints from SIPI
> >> and S3 (cant remember which one is the 4k constraint, but it's in the
> >> comments).
> > What you're talking about is the copy of the trampoline code/data in
> > low memory. trampoline_{start,end} themselves point into the Xen image.
> 
> True, but we're operating on bootsym_phys(trampoline_start) which had
> better be aligned.
> 
> We hard-code (by virtue of only filling in 1 single 4k PTE in the
> pagetables) that the AP trampoline is 4k.
> 
> The range here should be 4k only too, or we're (falsely) marking lowmem
> adjacent to the AP trampoline as a Xen range when it's not.

Hm, looking at zap_low_mappings() we do seem to possibly map more than
one page, in fact on my current build trampoline_end -
trampoline_start is 6528.

Thanks, Roger.