linux-kernel - Re: [PATCH v2 2/2] memblock: do not start bottom-up allocations with kernel

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Date:   Mon, 25 Jan 2021 21:30:55 -0300
From:   Thiago Jung Bauermann <bauerman@...ux.ibm.com>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, guro@...com,
        iamjoonsoo.kim@....com, Ram Pai <linuxram@...ibm.com>,
        Konrad Rzeszutek Wilk <konrad@...nok.org>,
        Satheesh Rajendran <sathnaga@...ux.vnet.ibm.com>,
        kernel-team@...com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        mhocko@...nel.org, riel@...riel.com
Subject: Re: [PATCH v2 2/2] memblock: do not start bottom-up allocations
 with kernel_end


Mike Rapoport <rppt@...nel.org> writes:

> On Sat, Jan 23, 2021 at 06:09:11PM -0800, Andrew Morton wrote:
>> On Fri, 22 Jan 2021 01:37:14 -0300 Thiago Jung Bauermann <bauerman@...ux.ibm.com> wrote:
>> 
>> > Mike Rapoport <rppt@...nel.org> writes:
>> > 
>> > > > Signed-off-by: Roman Gushchin <guro@...com>
>> > > 
>> > > Reviewed-by: Mike Rapoport <rppt@...ux.ibm.com>
>> > 
>> > I've seen a couple of spurious triggers of the WARN_ONCE() removed by this
>> > patch. This happens on some ppc64le bare metal (powernv) server machines with
>> > CONFIG_SWIOTLB=y and crashkernel=4G, as described in a candidate patch I posted
>> > to solve this issue in a different way:
>> > 
>> > https://lore.kernel.org/linuxppc-dev/20201218062103.76102-1-bauerman@linux.ibm.com/
>> > 
>> > Since this patch solves that problem, is it possible to include it in the next
>> > feasible v5.11-rcX, with the following tag?
>> 
>> We could do this,

Thanks!

>> if we're confident that this patch doesn't depend on
>> [1/2] "mm: cma: allocate cma areas bottom-up"?  I think it is...
>
> A think it does not depend on cma bottom-up allocation, it's rather the other
> way around: without this CMA bottom-up allocation could fail with KASLR
> enabled.

I agree. Conceptually, this could have been patch 1 in this series.

> Still, this patch may need updates to the way x86 does early reservations:
>
> https://lore.kernel.org/lkml/20210115083255.12744-1-rppt@kernel.org

Ah, I wasn't aware of this. Thanks for fixing those issues. That series
seems to be well accepted.

>> > Fixes: 8fabc623238e ("powerpc: Ensure that swiotlb buffer is allocated from low memory")
>> 
>> I added that.

Thanks!
-- 
Thiago Jung Bauermann
IBM Linux Technology Center