Re: [Xen-devel] Design doc of adding ACPI support for arm64 on Xen - version 5

[Shannon Zhao <shannon.zhao@xxxxxxxxxx>]

On 2015/9/2 19:09, Julien Grall wrote:
> On 02/09/15 07:02, Shannon Zhao wrote:
> > On 2015/9/1 21:40, Julien Grall wrote:
> > > On 01/09/15 13:35, Shannon Zhao wrote:
> > > > On 2015/9/1 19:28, Julien Grall wrote:
> > > > > Hi Shannon,
> > > > > On 01/09/15 05:12, Shannon Zhao wrote:
> > > > > > I tried this. Directly use the "kinfo->gnttab_start = __pa(_stext)" as
> > > > > > the address where these tables are mapped to Dom0. But the value of
> > > > > > gnttab_start is lower than the start of RAM, so Dom0 ingore these
> > > > > > regions and boot failed. see early_init_dt_add_memory_arch()
> > > > > Can you elaborate? How Linux will fail? If this region is marked as
> > > > > reserved in the UEFI memory map, Linux will mark the memory as reserved.
> > > > >
> > > > > Furthermore, *ioremap is used in order to map the EFI tables so I don't
> > > > > see a reason to fail.
> > > > It's fine to parse EFI table but fails to parse ACPI table.
> > > >
> > > > It doesn't add the memblock since it doesn't pass below check in
> > > > early_init_dt_add_memory_arch:
> > > >         if (base + size < phys_offset) {
> > > >                 pr_warning("Ignoring memory block 0x%llx - 0x%llx\n",
> > > >                            base, base + size);
> > > >                 return;
> > > >         }
> > > >
> > > > It's due to kinfo->gnttab_start (e.g. 0x87e00000) lower than the memory
> > > > start address (e.g. 0x90000000).
> > > >
> > > > Then Linux will fail at parsing ACPI table.
> > > >
> > > > ACPI: Interpreter enabled
> > > > ACPI: Using GIC for interrupt routing
> > > > Unhandled fault: alignment fault (0x96000021) at 0xffffff8000068184
> > > > Internal error: : 96000021 [#1] PREEMPT SMP
> > > > Modules linked in:
> > > > CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.2.0-rc6+ #143
> > > > Hardware name: (null) (DT)
> > > > task: ffffffc008870000 ti: ffffffc00884c000 task.ti: ffffffc00884c000
> > > > PC is at acpi_get_phys_id+0x264/0x290
> > > > LR is at acpi_get_phys_id+0x178/0x290
> > > IIRC, this is because Linux will consider the region as non-RAM (see
> > > acpi_os_ioremap in arch/arm64/include/asm/acpi.h).
> > >
> > > IHMO this is not a problem in the design but a bug in Linux/Xen.
> > >
> > > You need to see how to make Linux see the region as a RAM (either by
> > > early_init_dt_add_memory_arch or memblock_reserve). This would mean
> > > either change the way you describe the region in the UEFI memory map or
> > > fix Linux.
> > There are some descriptions in Documentation/arm64/booting.txt of Linux:
> >
> > "The Image must be placed text_offset bytes from a 2MB aligned base
> > address near the start of usable system RAM and called there. Memory
> > below that base address is currently unusable by Linux, and therefore it
> > is strongly recommended that this location is the start of system RAM.
> > At least image_size bytes from the start of the image must be free for
> > use by the kernel."
> >
> >  From this, it says "Memory below that base address is currently unusable
> > by Linux". So if we put these tables below Dom0 RAM address and even
> > describe these regions as RAM, the Linux could not use them.
> >
> > Any thoughts about this?
> Hold on, this is about Linux able to use the memory for his own usage.
> ACPI table are not part of this memory because they are marked reserved
> by the firmware.
>
> If we follow your logic, all ACPI tables always should be above the
> kernel. I don't believe this is the case and it would be buggy on Xen
> because of the DOM0 direct RAM mapping (i.e the first RAM bank can be
> very high and the kernel too).
It looks weird. But from the booting.txt, it says the memory below base 
address is unusable and from early_init_dt_add_memory_arch in Linux, it 
really ignores the memblock below the PAGE_OFFSET.
> I think the problem is how you reserved this region in the EFI memory
> table. From what I saw, you marked this new memory with EFI_MEMORY_WB
> (which means that the region can be usable by Linux).
Yes, I mark it with EFI_MEMORY_WB. Is this right?

--
Shannon

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel