Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:7 as permitted sender) client-ip=2620:137:e000::3:7;
Message-ID: <9be0159e-1762-6c07-e6eb-a86f1c780118@suse.cz>
Date:   Tue, 28 Nov 2023 12:25:28 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.15.1
Subject: Re: [PATCH v2] efi/unaccepted: Fix off-by-one when checking for
 overlapping ranges
Content-Language: en-US
To:     Ard Biesheuvel <ardb@kernel.org>
Cc:     Michael Roth <michael.roth@amd.com>, linux-efi@vger.kernel.org,
        x86@kernel.org, linux-coco@lists.linux.dev, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Nikolay Borisov <nik.borisov@suse.com>, stable@kernel.org,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Paolo Bonzini <pbonzini@redhat.com>
References: <20231103151354.110636-1-michael.roth@amd.com>
 <30ff0335-3d9c-7d54-85d0-5898320f4e1f@suse.cz>
 <CAMj1kXF-B_1MJahfFg72cgcmZ9dMvqiEm8WGGejkqRFN=JreEA@mail.gmail.com>
From:   Vlastimil Babka <vbabka@suse.cz>
In-Reply-To: <CAMj1kXF-B_1MJahfFg72cgcmZ9dMvqiEm8WGGejkqRFN=JreEA@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 11/8/23 12:21, Ard Biesheuvel wrote:
> On Fri, 3 Nov 2023 at 16:30, Vlastimil Babka <vbabka@suse.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@linux.intel.com>
>> > Signed-off-by: Michael Roth <michael.roth@amd.com>
>>
>> More justification for introducing a common ranges_overlap() helper somewhere :)
>>
>> Acked-by: Vlastimil Babka <vbabka@suse.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;
>>
>