linux-kernel - Re: [PATCH] lib/logic_pio: Fix overlap check for pio registery

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Date:   Fri, 15 Jan 2021 10:10:58 +0000
From:   John Garry <john.garry@...wei.com>
To:     Jiahui Cen <cenjiahui@...wei.com>, <linux-kernel@...r.kernel.org>
CC:     Wei Xu <xuwei5@...ilicon.com>, Arnd Bergmann <arnd@...db.de>,
        "Bjorn Helgaas" <bhelgaas@...gle.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        <xieyingtai@...wei.com>,
        "linuxarm@...neuler.org" <linuxarm@...neuler.org>
Subject: Re: [PATCH] lib/logic_pio: Fix overlap check for pio registery

On 21/12/2020 13:04, Jiahui Cen wrote:
>> On 21/12/2020 03:24, Jiahui Cen wrote:
>>> Hi John,
>>>
>>> On 2020/12/18 18:40, John Garry wrote:
>>>> On 18/12/2020 06:23, Jiahui Cen wrote:
>>>>> Since the [start, end) is a half-open interval, a range with the end equal
>>>>> to the start of another range should not be considered as overlapped.
>>>>>
>>>>> Signed-off-by: Jiahui Cen<cenjiahui@...wei.com>
>>>>> ---
>>>>>     lib/logic_pio.c | 2 +-
>>>>>     1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/lib/logic_pio.c b/lib/logic_pio.c
>>>>> index f32fe481b492..445d611f1dc1 100644
>>>>> --- a/lib/logic_pio.c
>>>>> +++ b/lib/logic_pio.c
>>>>> @@ -57,7 +57,7 @@ int logic_pio_register_range(struct logic_pio_hwaddr *new_range)
>>>>>                 new_range->flags == LOGIC_PIO_CPU_MMIO) {
>>>>>                 /* for MMIO ranges we need to check for overlap */
>>>>>                 if (start >= range->hw_start + range->size ||
>>>>> -                end < range->hw_start) {
>>>>> +                end <= range->hw_start) {
>>>> It looks like your change is correct, but should not really have an impact in practice since:
>>>> a: BIOSes generally list ascending IO port CPU addresses
>>>> b. there is space between IO port CPU address regions
>>>>
>>>> Have you seen a problem here?
>>>>
>>> No serious problem. I found it just when I was working on adding support of
>>> pci expander bridge for Arm in QEMU. I found the IO window of some extended
>>> root bus could not be registered when I inserted the extended buses' _CRS
>>> info into DSDT table in the x86 way, which does not sort the buses.
>>>
>>> Though root buses should be sorted in QEMU, would it be better to accept
>>> those non-ascending IO windows?
>>>
>> ok, so it seems that you have seen a real problem, and this issue is not just detected by code analysis.
>>
>>> BTW, for b, it seems to be no space between IO windows of different root buses
>>> generated by EDK2. Or maybe I missed something obvious.
>> I don't know about that. Anyway, your change looks ok.
>>
>> Reviewed-by: John Garry<john.garry@...wei.com>
>>
>> BTW, for your virt env, will there be requirement to unregister PCI MMIO ranges? Currently we don't see that in non-virt world.
>>
> Thanks for your review.
> 
> And currently there is no such a requirement in my virt env.
> 

I am not sure what happened to this patch, but I plan on sending some 
patches in this area soon - do you want me to include this one?

Thanks,
John