Re: [RFC PATCH v2 1/3] resource: Request IO port regions from children of ioport_resource

From: John Garry
Date: Wed Mar 27 2019 - 07:24:54 EST

On 26/03/2019 22:48, Bjorn Helgaas wrote:
[+cc Catalin, Will, linux-arm-kernel]

From my checking, the f71882fg hwmon is accessed via the super-io interface
on the PCH on x86. The super-io interface is at fixed addresses, those being
0x2e and 0x4e.

Please see the following:

(Table 9.2).

On x86 systems, these PCH IO ports will be mapped on a PCI bus, like:

$more /proc/ioports
0000-0cf7 : PCI Bus 0000:00
0000-001f : dma1
0020-0021 : pic1
0040-0043 : timer0
0050-0053 : timer1
0060-0060 : keyboard
0064-0064 : keyboard
0070-0077 : rtc0
0080-008f : dma page reg
00a0-00a1 : pic2
00c0-00df : dma2
00f0-00ff : fpu

So, the idea in the patch is that if PCI Bus 0000:00 does not exist because
of no PCI host, then we should fail a request to an IO port region.

Hi Bjorn,

I'm not convinced about this last sentence.

It's true that on most modern systems, including that Intel PCH, the
Super I/O controller is attached via an LPC bridge on a PCI bus.

But I don't think it's an actual requirement that PCI be involved.
There certainly once were systems, e.g., PC/104, that had ISA devices
but no PCI. Maybe Super I/O attached via ISA is obsolete enough that
we don't care any more, but I really don't know.

OK, fine. So if this is true, then this patch falls apart.

However I don't know for sure either. I would still like to think that these legacy ISA system should still insert a bus resource under ioport_resource, from which devices on that bus should request resources.

On x86, I think inb/inw/inl from a port where nothing responds
probably just returns ~0, and outb/outw/outl just get dropped.
Shouldn't arm64 do the same, without crashing?

That would be ideal and we're doing something similar in patch 2/3.

So on ARM64 we have to IO remap the PCI IO resource. If this mapping is not
done (due to no PCI host), then any inb/inw/inl calls will crash the system.

My take is that ARM64 is responsible for implementing inb/inw/inl in
such a way that they don't crash. I don't think it's practical to
update all the old ISA drivers or even the core code to work around

As I mentioned below, I was actually also fixing up inb/inw/inl et al for arm64 such that they don't crash the system in this case. This was in patch 2/3.

So on arm64 - which defines PCI_IOBASE - we need to IO remap the PCI IO space resource. If this is not done and we access PCI IO space, then we crash.

However with the introduction of logical PIO space in commit 031e3601869c, we can test this mapping by ensuring that we have a logical PIO region registered. If there is none, then we can discard the access.

However this would only be for when INDIRECT_PIO is defined. Maybe I can make it work for when INDIRECT_PIO is not defined, or even drop !INDIRECT_PIO support.

A final note on hwmon f71882fg: even with the change in 2/3, this driver still accesses IO ports 0x2e and 0x4e, which would not be a PCH fixed IO port on !x86 systems, so far from ideal.

I saw that in commit 746cdfbf01c0 ("hwmon: Avoid building drivers for powerpc that read/write ISA addresses"), PPC would not build these drivers, as, like arm, it has no native ISA.

So in patch 2/3, I am also making the change to the logical PIO inb/inw/inl
accessors to discard accesses when no PCI MMIO regions are registered in
logical PIO space.

This is really a second line of defense (this patch being the first).

root@(none)$root@(none)$ insmod f71882fg.ko
[ 152.215377] Unable to handle kernel paging request at virtual address ffff7dfffee0002e
[ 152.231299] Mem abort info:
[ 152.236898] ESR = 0x96000046
[ 152.243019] Exception class = DABT (current EL), IL = 32 bits
[ 152.254905] SET = 0, FnV = 0
[ 152.261024] EA = 0, S1PTW = 0
[ 152.267320] Data abort info:
[ 152.273091] ISV = 0, ISS = 0x00000046
[ 152.280784] CM = 0, WnR = 1
[ 152.286730] swapper pgtable: 4k pages, 48-bit VAs, pgdp = (____ptrval____)
[ 152.300537] [ffff7dfffee0002e] pgd=000000000141c003, pud=000000000141d003, pmd=0000000000000000
[ 152.318016] Internal error: Oops: 96000046 [#1] PREEMPT SMP
[ 152.329199] Modules linked in: f71882fg(+)
[ 152.337415] CPU: 8 PID: 2732 Comm: insmod Not tainted 5.1.0-rc1-00002-gab1a0e9200b8-dirty #102
[ 152.354712] Hardware name: Huawei Taishan 2280 /D05, BIOS Hisilicon D05 IT21 Nemo 2.0 RC0 04/18/2018
[ 152.373058] pstate: 80000005 (Nzcv daif -PAN -UAO)
[ 152.382675] pc : logic_outb+0x54/0xb8
[ 152.390017] lr : f71882fg_find+0x64/0x390 [f71882fg]
[ 152.399977] sp : ffff000013393aa0
[ 152.406618] x29: ffff000013393aa0 x28: ffff000008b98b10
[ 152.417278] x27: ffff000013393df0 x26: 0000000000000100
[ 152.427938] x25: ffff801f8c872d30 x24: ffff000011420000
[ 152.438598] x23: ffff801fb49d2940 x22: ffff000011291000
[ 152.449257] x21: 000000000000002e x20: 0000000000000087
[ 152.459917] x19: ffff000013393b44 x18: ffffffffffffffff
[ 152.470577] x17: 0000000000000000 x16: 0000000000000000
[ 152.481236] x15: ffff00001127d6c8 x14: ffff801f8cfd691c
[ 152.491896] x13: 0000000000000000 x12: 0000000000000000
[ 152.502555] x11: 0000000000000003 x10: 0000801feace2000
[ 152.513215] x9 : 0000000000000000 x8 : ffff841fa654f280
[ 152.523874] x7 : 0000000000000000 x6 : 0000000000ffc0e3
[ 152.534534] x5 : ffff000011291360 x4 : ffff801fb4949f00
[ 152.545194] x3 : 0000000000ffbffe x2 : 76e767a63713d500
[ 152.555853] x1 : ffff7dfffee0002e x0 : ffff7dfffee00000
[ 152.566514] Process insmod (pid: 2732, stack limit = 0x(____ptrval____))
[ 152.579968] Call trace:
[ 152.584863] logic_outb+0x54/0xb8
[ 152.591506] f71882fg_find+0x64/0x390 [f71882fg]
[ 152.600768] f71882fg_init+0x38/0xc70 [f71882fg]
[ 152.610031] do_one_initcall+0x5c/0x198
[ 152.617723] do_init_module+0x54/0x1b0
[ 152.625237] load_module+0x1dc4/0x2158
[ 152.632752] __se_sys_init_module+0x14c/0x1e8
[ 152.641490] __arm64_sys_init_module+0x18/0x20
[ 152.650404] el0_svc_common+0x5c/0x100
[ 152.657919] el0_svc_handler+0x2c/0x80
[ 152.665433] el0_svc+0x8/0xc
[ 152.671202] Code: d2bfdc00 f2cfbfe0 f2ffffe0 8b000021 (39000034)
[ 152.683434] ---[ end trace fd4f35b610829a48 ]---
Segmentation fault

Note that the f71882fg driver correctly calls request_muxed_region().

This issue was originally reported in [1].

This patch changes the functionality of request{muxed_}_region() to
request a region from a direct child descendent of the top

In this, if the IO port region has not been mapped for a particular IO
region, the PCI IO resource would also not have been inserted, and so a
suitable child region will not exist. As such,
request_{muxed_}region() calls will fail.

A side note: there are many drivers in the kernel which fail to even call
request_{muxed_}region() prior to IO port accesses, and they also need to
be fixed (to call request_{muxed_}region(), as appropriate) separately.


Please use a URL instead of

ok, I hope that I can find this old thread.

The beauty of is that the URL contains the Message-ID, so
it's easy build the URL and it would contain useful information even if disappeared:

ok, great.

Thanks again,