[PATCH 0/8] arm64: improved memory map handling for /dev/mem, ACPI etc

[Ard Biesheuvel]

On 4 January 2015 at 08:19, Dave Young <dyoung at redhat.com> wrote:
> On 12/30/14 at 01:21pm, Ard Biesheuvel wrote:
>> On 30 December 2014 at 09:25, Dave Young <dyoung at redhat.com> wrote:
>> > On 12/29/14 at 09:22am, Ard Biesheuvel wrote:
>> >> On 26 December 2014 at 09:35, Dave Young <dyoung at redhat.com> wrote:
>> >> > On 12/22/14 at 07:08pm, Ard Biesheuvel wrote:
>> >> >> This series was split off from the UEFI virtmap for kexec series that I posted
>> >> >> earlier today. The main purpose is to deal with the need to classify memory
>> >> >> ranges as RAM or non-RAM in a consistent and comprehensive manner. This series
>> >> >> applies on top of the other series.
>> >> >>
>> >> >> Patch #1 avoids an early panic if the UEFI memory map is available but UEFI
>> >> >> support itself fails to initialize. In this case, there is no need to panic
>> >> >> early, and we have a better chance of being able to inform the user if we deal
>> >> >> with this error condition at a later time.
>> >> >>
>> >> >> Patch #2 adds iomem resource registration of UEFI memory regions. This is
>> >> >> necessary because otherwise, drivers could potentially claim regions that
>> >> >> are in active use by the firmware. This applies to both MMIO (NOR flash, RTC)
>> >> >> and RAM ranges (runtime services code and data).
>> >> >>
>> >> >> Patch #3-6 adds support to UEFI and non-UEFI code paths to record all memory
>> >> >> known to the system in the 'physmem' memblock table (if enabled). This fulfils
>> >> >> a need in the /dev/mem and (upcoming) ACPI layers to be able to classify ranges
>> >> >> as being backed by normal RAM even if they are not covered by the 'memory'
>> >> >> memblock table, and are hence not covered by the linear direct mapping.
>> >> >> The physmem code is pre-existing code that only needs minor tweaking to be made
>> >> >> suitable for this purpose.
>> >> >>
>> >> >> Patch #7 enables the 'physmem' memblock table for arm64, and wires it into the
>> >> >> handling of /dev/mem mappings, both to decide whether it should be mapped as
>> >> >> MT_NORMAL, and whether read-write access can be allowed. (Non-RAM regions can
>> >> >> be mapped read-write as long as they are not claimed by a driver in the iomem
>> >> >> resource table. RAM regions can only be mapped read-only, and only if they are
>> >> >> not covered by the 'memory' memblock table, and hence not covered by the linear
>> >> >> mapping)
>> >> >>
>> >> >> Finally, patch #8 changes the way the virtual memory map is handled by the
>> >> >> early UEFI code. Specifically, it memblock_remove()s rather than _reserves()
>> >> >> UEFI reserved RAM regions, so that they are removed entirely from the linear
>> >> >> mapping.
>> >> >>
>> >> >> Ard Biesheuvel (8):
>> >> >>   arm64/efi: use UEFI memory map unconditionally if available
>> >> >>   arm64/efi: register UEFI reserved regions as iomem resources
>> >> >>   memblock: add physmem to memblock_dump_all() output
>> >> >>   memblock: introduce memblock_add_phys() and memblock_is_physmem()
>> >> >>   of: fdt: register physmem in early_init_dt_scan_memory()
>> >> >>   arm64/efi: register physmem in reserve_regions()
>> >> >>   arm64: use 'physmem' memblock to improve CONFIG_STRICT_DEVMEM handling
>> >> >>   arm64/efi: memblock_remove rather than _reserve UEFI reserved RAM
>> >> >
>> >> > Ard, It is much cleaner for this splitting.
>> >> >
>> >>
>> >> Thanks for having a look.
>> >>
>> >> > I wonder if some of them can become general code such as register reserved
>> >> > regions as iomem resources?
>> >> >
>> >>
>> >> AFAICT, the x86 code adds reservations for such regions to the E820
>> >> memory map, which in turn is used to memblock_reserve() the actual
>> >> memory. Also, sharing of the RTC is handled with a dedicated mutex in
>> >> the runtime services wrapper code (and x86 does not even use the time
>> >> related runtime services as they are broken on many firmware
>> >> implementations) so blindly applying the same logic to x86 or ia64
>> >> would likely break stuff.
>> >
>> > Ok, I think bootloader will pass the E820 ranges though it can not tell
>> > which region is for what.
>> >
>> >>
>> >> Do you (or Mark) have any feedback on the utility of this series in
>> >> the ACPI context? I failed to mention in the cover letter that
>> >> memblock_is_physmem() now serves the purpose of page_is_ram(), i.e.,
>> >> whether a physical region is backed by a slice of RAM that was left
>> >> out of the kernel's linear mapping.
>> >
>> > I will do some test later along with the stable mapping stuff.
>
> The whole patchset works well without the last patch.
>
> I found that patch 8/8 caused system boot hangs very early.
> Just after stub print something about virtmap..
>

Which platform is this?
Do you have earlycon enabled?

> Any idea about it? I tested your patches upon 3.18.
>

I suppose you tested both the virtmap series and this one, but did you
also take the 3.19 changes we did for UEFI? Not sure it would make a
difference, though.

>> > BTW, with previous stable mapping patches on modified 3.18 tree kexec kernel
>> > panics because of damaged efi mempry map arrays. It contains some
>> > random value instead of right addresses so that virt_to_phys return
>> > same value for vendor field. Will do more debugging maybe I missed something.
>> > Any clue for debugging above issue will be appreciated.
>> >
>>
>> No clues, unfortunately. The memory map is not used after early boot,
>> so it may be getting clobbered at any point between the first boot and
>> the second boot.
>
> It was caused by uefi sys table/mmap start addresses changes.
> I generate dtb from acpi=off boot /proc/device-tree, and use the dtb for kexec
> boot, but seems mmap addresses changes sometimes.
>
> Do you know have plan or status in Linaro for exporting dtb for acpi booting?
>

We have this patch upstream now

08d53aa58cb1 of/fdt: export fdt blob as /sys/firmware/fdt

which exports whatever FDT the kernel received from the bootloader or
the EFI stub, regardless of whether the kernel uses DT or not.

-- 
Ard.