linux-kernel - Re: [PATCH 3/3] PCI: designware-ep: Return an error when requesting a too large BAR size

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Date:   Tue, 6 Feb 2018 21:38:09 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Niklas Cassel <niklas.cassel@...s.com>
Cc:     Jingoo Han <jingoohan1@...il.com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] PCI: designware-ep: Return an error when requesting a
 too large BAR size

On Mon, Feb 5, 2018 at 6:25 PM, Niklas Cassel <niklas.cassel@...s.com> wrote:
> On Thu, Feb 01, 2018 at 02:00:40PM -0500, Jingoo Han wrote:
>> On Thursday, February 1, 2018 1:58 PM, Andy Shevchenko wrote:
>> >
>> > On Thu, Feb 1, 2018 at 6:11 PM, Niklas Cassel <niklas.cassel@...s.com>
>> > wrote:
>> >
>> > include/linux/sizes.h:
>> >
>> > +SZ_4G  0x100000000ULL
>> >
>> > > +       if (size > 0x100000000ULL) {
>> >
>> > #include <linux/sizes.h>
>> >
>> > if (size > SZ_4G) {
>>
>> I like this one for the readability.
>> Thank you.
>>
>
> I liked it too, however both variants
>
> if (size > 0x100000000ULL) {
>
> if (size > SZ_4G) {
>
> result in:
>
> drivers/pci/dwc/pcie-designware-ep.c:131:11: warning:
>   comparison is always false due to limited range of data type [-Wtype-limits]
>
> when compiling with W=1 on a platform with 32-bit size_t.
>
>
> The annoying thing here is that a BAR can be 64-bit,
> yet the parameter size is defined as a size_t,
> so the error will only show on 32-bit and not on 64-bit.

Oh, indeed. And it looks moving to u64 or alike is not a solution
(because if would not describe real hardware in that case).

> What do you think about:

> if (upper_32_bits(size)) {
>         dev_err(pci->dev, "can't handle BAR larger than 4GB\n");
>         return -EINVAL;
> }
>
> That should compile without warnings for both
> 32-bit size_t and 64-bit size_t.

Can you derive some helper based on the code in __pci_read_base() code?

-- 
With Best Regards,
Andy Shevchenko