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

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Date:   Mon, 21 Dec 2020 11:12:54 +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>
Subject: Re: [PATCH] lib/logic_pio: Fix overlap check for pio registery

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,
John