On Wed, Oct 18, 2023 at 05:11:58PM +0200, Jan Beulich wrote:
> On 17.10.2023 10:29, Roger Pau Monne wrote:
> > The mapping of memory regions below the 1MB mark was all done by the PVH
> > dom0
> > builder code, causing the region to be avoided by the arch specific IOMMU
> > hardware domain initialization code. That lead to the IOMMU being enabled
> > without reserved regions in the low 1MB identity mapped in the p2m for PVH
> > hardware domains. Firmware which happens to be missing RMRR/IVMD ranges
> > describing E820 reserved regions in the low 1MB would transiently trigger
> > IOMMU
> > faults until the p2m is populated by the PVH dom0 builder:
> >
> > AMD-Vi: IO_PAGE_FAULT: 0000:00:13.1 d0 addr 00000000000eb380 flags 0x20 RW
> > AMD-Vi: IO_PAGE_FAULT: 0000:00:13.1 d0 addr 00000000000eb340 flags 0
> > AMD-Vi: IO_PAGE_FAULT: 0000:00:13.2 d0 addr 00000000000ea1c0 flags 0
> > AMD-Vi: IO_PAGE_FAULT: 0000:00:14.5 d0 addr 00000000000eb480 flags 0x20 RW
> > AMD-Vi: IO_PAGE_FAULT: 0000:00:12.0 d0 addr 00000000000eb080 flags 0x20 RW
> > AMD-Vi: IO_PAGE_FAULT: 0000:00:14.5 d0 addr 00000000000eb400 flags 0
> > AMD-Vi: IO_PAGE_FAULT: 0000:00:12.0 d0 addr 00000000000eb040 flags 0
> >
> > Those errors have been observed on the osstest pinot{0,1} boxes (AMD Fam15h
> > Opteron(tm) Processor 3350 HE).
> >
> > Rely on the IOMMU arch init code to create any identity mappings for
> > reserved
> > regions in the low 1MB range (like it already does for reserved regions
> > elsewhere), and leave the mapping of any holes to be performed by the dom0
> > builder code.
> >
> > Fixes: 6b4f6a31ace1 ('x86/PVH: de-duplicate mappings for first Mb of Dom0
> > memory')
> > Signed-off-by: Roger Pau Monné <[email protected]>
>
> Reviewed-by: Jan Beulich <[email protected]>
> with one suggestion:
>
> > --- a/xen/arch/x86/hvm/dom0_build.c
> > +++ b/xen/arch/x86/hvm/dom0_build.c
> > @@ -449,7 +449,7 @@ static int __init pvh_populate_p2m(struct domain *d)
> > }
> > }
> >
> > - /* Non-RAM regions of space below 1MB get identity mapped. */
> > + /* Identity map everything below 1MB that's not already mapped. */
> > for ( i = rc = 0; i < MB1_PAGES; ++i )
> > {
> > p2m_type_t p2mt;
> > @@ -459,8 +459,8 @@ static int __init pvh_populate_p2m(struct domain *d)
> > rc = set_mmio_p2m_entry(d, _gfn(i), _mfn(i), PAGE_ORDER_4K);
> > else
> > /*
> > - * If the p2m entry is already set it must belong to a RMRR and
> > - * already be identity mapped, or be a RAM region.
> > + * If the p2m entry is already set it must belong to a
> > RMRR/IVMD or
> > + * reserved region and be identity mapped, or else be a RAM
> > region.
> > */
> > ASSERT(p2mt == p2m_ram_rw || mfn_eq(mfn, _mfn(i)));
>
> Would you mind wording the comment slightly differently, e.g.
>
> "If the p2m entry is already set it must belong to a reserved region
> (e.g. RMRR/IVMD) and be identity mapped, or else be a RAM region."
>
> This is because such RMRR/IVMD regions are required to be in reserved
> ranges anyway.
IIRC there's an option to provide extra RMRR/IVMD regions on the
command line, and those are not required to be on reserved regions?
Otherwise LGTM, so would you mind adjusting at commit?
Thanks, Roger.
