Date:   Tue, 26 Mar 2019 17:48:10 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     John Garry <john.garry@...wei.com>
Cc:     rafael@...nel.org, arnd@...db.de, lorenzo.pieralisi@....com,
        bp@...e.de, linux@...ck-us.net, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, wangkefeng.wang@...wei.com,
        linuxarm@...wei.com, andy.shevchenko@...il.com,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH v2 1/3] resource: Request IO port regions from
 children of ioport_resource

[+cc Catalin, Will, linux-arm-kernel]

On Tue, Mar 26, 2019 at 04:33:55PM +0000, John Garry wrote:
> On 25/03/2019 23:32, Bjorn Helgaas wrote:
> > On Thu, Mar 21, 2019 at 02:14:08AM +0800, John Garry wrote:
> > > Currently when we request an IO port region, the request is made directly
> > > to the top resource, ioport_resource.
> > 
> > Let's be explicit here, e.g.,
> > 
> >   Currently request_region() requests an IO port region directly from the
> >   top resource, ioport_resource.
> 
> ok
> 
> > > There is an issue here, in that drivers may successfully request an IO
> > > port region even if the IO port region has not even been mapped in
> > > (in pci_remap_iospace()).
> > > 
> > > This may lead to crashes when the system has no PCI host, or, has a host
> > > but it has failed enumeration, while drivers still attempt to access PCI
> > > IO ports, as below:
> > 
> > I don't understand the strategy here.  f71882fg is not a driver for a
> > PCI device, so it should work even if there is no PCI host in the
> > system.
> 
> 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:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/hwmon/f71805f.c?h=v5.1-rc2#n1621
> 
> and
> 
> https://www.intel.com/content/dam/www/public/us/en/documents/datasheets/8-series-chipset-pch-datasheet.pdf
> (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.

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.

> > 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
that.

> 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
> > > root@(none)$
> > 
> > > 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
> > > ioport_resource.
> > > 
> > > 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.
> > > 
> > > [1] https://www.spinics.net/lists/linux-pci/msg49821.html
> > 
> > Please use a https://lore.kernel.org/ URL instead of spinics.net.
> 
> ok, I hope that I can find this old thread.

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

https://lore.kernel.org/linux-pci/56F209A9.4040304@huawei.com

Bjorn

> > > Signed-off-by: John Garry <john.garry@...wei.com>
> > > ---
> 
> Thanks!
> 
> > >  include/linux/ioport.h | 12 +++++++++---
> > >  kernel/resource.c      | 28 ++++++++++++++++++++++++++++
> > >  2 files changed, 37 insertions(+), 3 deletions(-)
> > > 
> 
> Leaving remaing text as a reference.
> 
> > > diff --git a/include/linux/ioport.h b/include/linux/ioport.h
> > > index da0ebaec25f0..d7b7e1e08291 100644
> > > --- a/include/linux/ioport.h
> > > +++ b/include/linux/ioport.h
> > > @@ -217,19 +217,25 @@ static inline bool resource_contains(struct resource *r1, struct resource *r2)
> > > 
> > > 
> > >  /* Convenience shorthand with allocation */
> > > -#define request_region(start,n,name)		__request_region(&ioport_resource, (start), (n), (name), 0)
> > > -#define request_muxed_region(start,n,name)	__request_region(&ioport_resource, (start), (n), (name), IORESOURCE_MUXED)
> > > +#define request_region(start,n,name)		__request_region_from_children(&ioport_resource, (start), (n), (name), 0)
> > > +#define request_muxed_region(start,n,name)	__request_region_from_children(&ioport_resource, (start), (n), (name), IORESOURCE_MUXED)
> > >  #define __request_mem_region(start,n,name, excl) __request_region(&iomem_resource, (start), (n), (name), excl)
> > >  #define request_mem_region(start,n,name) __request_region(&iomem_resource, (start), (n), (name), 0)
> > >  #define request_mem_region_exclusive(start,n,name) \
> > >  	__request_region(&iomem_resource, (start), (n), (name), IORESOURCE_EXCLUSIVE)
> > >  #define rename_region(region, newname) do { (region)->name = (newname); } while (0)
> > > 
> > > -extern struct resource * __request_region(struct resource *,
> > > +extern struct resource *__request_region(struct resource *,
> > >  					resource_size_t start,
> > >  					resource_size_t n,
> > >  					const char *name, int flags);
> > > 
> > > +extern struct resource *__request_region_from_children(struct resource *,
> > > +					resource_size_t start,
> > > +					resource_size_t n,
> > > +					const char *name, int flags);
> > > +
> > > +
> > >  /* Compatibility cruft */
> > >  #define release_region(start,n)	__release_region(&ioport_resource, (start), (n))
> > >  #define release_mem_region(start,n)	__release_region(&iomem_resource, (start), (n))
> > > diff --git a/kernel/resource.c b/kernel/resource.c
> > > index 92190f62ebc5..87ed200eda8b 100644
> > > --- a/kernel/resource.c
> > > +++ b/kernel/resource.c
> > > @@ -1097,6 +1097,34 @@ resource_size_t resource_alignment(struct resource *res)
> > > 
> > >  static DECLARE_WAIT_QUEUE_HEAD(muxed_resource_wait);
> > > 
> > > +/**
> > > + * __request_region_from_children - create a new busy region from a child
> > > + * @parent: parent resource descriptor
> > > + * @start: resource start address
> > > + * @n: resource region size
> > > + * @name: reserving caller's ID string
> > > + * @flags: IO resource flags
> > > + */
> > > +struct resource *__request_region_from_children(struct resource *parent,
> > > +						resource_size_t start,
> > > +						resource_size_t n,
> > > +						const char *name, int flags)
> > > +{
> > > +	struct resource *res = __request_region(parent, start, n, name, flags);
> > > +
> > > +	if (res && res->parent == parent) {
> > > +		/*
> > > +		 * This is a direct descendent of the parent, which is
> > > +		 * what we didn't want.
> > > +		 */
> > > +		__release_region(parent, start, n);
> > > +		res = NULL;
> > > +	}
> > > +
> > > +	return res;
> > > +}
> > > +EXPORT_SYMBOL(__request_region_from_children);
> > > +
> > >  /**
> > >   * __request_region - create a new busy resource region
> > >   * @parent: parent resource descriptor
> > > --
> > > 2.17.1
> > > 
> > 
> > .
> > 
> 
> 

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