Re: [Xen-devel] [PATCH RFC 31/35] arm : acpi map status override table to dom0

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Parth,

On 05/02/2015 18:57, Parth Dixit wrote:
> On 5 February 2015 at 10:54, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
> > On 04/02/2015 14:02, parth.dixit@xxxxxxxxxx wrote:
> > > +    stao->header.length = sizeof(struct acpi_table_header) + 1;
> > > +    stao->header.checksum = 0;
> > > +    ACPI_MEMCPY(stao->header.oem_id, "LINARO", 6);
> > > +    ACPI_MEMCPY(stao->header.oem_table_id, "RTSMVEV8", 8);
> >
> > I though the plan was to use a Xen OEM ID?
> yes, but its not clear what should be used as xen oem id is not finalized yet.
I though we decided a name on the email, what is missing?

> > > +    stao->header.revision = 1;
> > > +    ACPI_MEMCPY(stao->header.asl_compiler_id, "INTL", 4);
> > > +    stao->header.asl_compiler_revision = 0x20140828;
> >
> > Where does this revision comes from?
> from the spec
What do you mean? I didn't know that the spec requires a specific 
compiler version... IHMO, this would be wrong.
> > > +    stao->uart = 1;
> >
> > What about the devpath?
> there is no table for devpath yet, it would require table specific handling
> (mostly parsing) and it can then be updated in it, or maybe i can
> create separate structure
> which can be used here but element would be added at runtime for each table.
> what do you think?
The devpath is a list of device blacklisted by path, right? If so, the 
comment on the field devpath is wrong. Also, it's defined as u8[1], 
which is very confusing.
> > > +    size = sizeof(struct acpi_table_stao);
> > > +    checksum = acpi_tb_checksum(ACPI_CAST_PTR(u8, stao), size);
> > > +    stao->header.checksum = (u8)( stao->header.checksum - checksum );
> >
> > No space before the last )
> >
> > > +    *mstao = addr = virt_to_maddr(stao);
> > > +
> > > +    res = map_ram_regions(d,
> > > +                          paddr_to_pfn(addr & PAGE_MASK),
> > > +                          DIV_ROUND_UP(size, PAGE_SIZE),
> > > +                          paddr_to_pfn(addr & PAGE_MASK));
> >
> > I'm concerned with this mapping, as long as most of the others.
> > map_ram_regions is mapping Read/Write the region. In this case, the STAO
> > size may not be aligned to PAGE_SIZE.
> >
> > So we may end up to map to DOM0 RW Xen memory. Even if DOM0 is a trusted
> > domain, we should never let DOM0 write in Xen memory.
> >
> > IIRC, the plan was to map at least RO all the ACPI tables.
> Sure, i'll map them to RO in next patchset.
I didn't say this is the right solution ;). It was something I recall 
from a discussion we had few months ago.
So before using this solution, can anyone (re-)confirm me that the ACPI 
tables should not be modified by the guest? If so, this should also be 
written somewhere for documentation purpose. It may save time in the 
future :).
Regards,

--
Julien Grall

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