linux-kernel - Re: [PATCH v2] efi/unaccepted: Fix off-by-one when checking for overlapping ranges

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Message-ID: <9be0159e-1762-6c07-e6eb-a86f1c780118@suse.cz>
Date:   Tue, 28 Nov 2023 12:25:28 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Michael Roth <michael.roth@....com>, linux-efi@...r.kernel.org,
        x86@...nel.org, linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Nikolay Borisov <nik.borisov@...e.com>, stable@...nel.org,
        Tom Lendacky <thomas.lendacky@....com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v2] efi/unaccepted: Fix off-by-one when checking for
 overlapping ranges

On 11/8/23 12:21, Ard Biesheuvel wrote:
> On Fri, 3 Nov 2023 at 16:30, Vlastimil Babka <vbabka@...e.cz> wrote:
>>
>> On 11/3/23 16:13, Michael Roth wrote:
>> > When a task needs to accept memory it will scan the accepting_list
>> > to see if any ranges already being processed by other tasks overlap
>> > with its range. Due to an off-by-one in the range comparisons, a task
>> > might falsely determine that an overlapping range is being accepted,
>> > leading to an unnecessary delay before it begins processing the range.
>> >
>> > Fix the off-by-one in the range comparison to prevent this and slightly
>> > improve performance.
>> >
>> > Fixes: 50e782a86c98 ("efi/unaccepted: Fix soft lockups caused by parallel memory acceptance")
>> > Link: https://lore.kernel.org/linux-mm/20231101004523.vseyi5bezgfaht5i@amd.com/T/#me2eceb9906fcae5fe958b3fe88e41f920f8335b6
>> > Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
>> > Signed-off-by: Michael Roth <michael.roth@....com>
>>
>> More justification for introducing a common ranges_overlap() helper somewhere :)
>>
>> Acked-by: Vlastimil Babka <vbabka@...e.cz>
>>
> 
> Thanks, I'll take this as a fix.

Ping, can't see it in mainline nor -next?

> 
>> > ---
>> > v2:
>> >  * Improve commit message terminology (Kirill)
>> > ---
>> >  drivers/firmware/efi/unaccepted_memory.c | 2 +-
>> >  1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/drivers/firmware/efi/unaccepted_memory.c b/drivers/firmware/efi/unaccepted_memory.c
>> > index 135278ddaf62..79fb687bb90f 100644
>> > --- a/drivers/firmware/efi/unaccepted_memory.c
>> > +++ b/drivers/firmware/efi/unaccepted_memory.c
>> > @@ -100,7 +100,7 @@ void accept_memory(phys_addr_t start, phys_addr_t end)
>> >        * overlap on physical address level.
>> >        */
>> >       list_for_each_entry(entry, &accepting_list, list) {
>> > -             if (entry->end < range.start)
>> > +             if (entry->end <= range.start)
>> >                       continue;
>> >               if (entry->start >= range.end)
>> >                       continue;
>>
>