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Message-ID: <ed2f59dc-ecd3-ae9c-e44c-81e903c6f08f@quicinc.com>
Date:   Tue, 28 Sep 2021 02:22:59 +0300
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Subject: Re: [RFC] arm64: mm: update max_pfn after memory hotplug
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To:     David Hildenbrand <david@redhat.com>,
        Chris Goldsworthy <quic_cgoldswo@quicinc.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        "Will Deacon" <will@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
CC:     <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
        Sudarshan Rajagopalan <quic_sudaraja@quicinc.com>
References: <cover.1632437225.git.quic_cgoldswo@quicinc.com>
 <595d09279824faf1f54961cef52b745609b05d97.1632437225.git.quic_cgoldswo@quicinc.com>
 <833493d2-d585-47ee-c258-79eae5deff36@redhat.com>
From:   Georgi Djakov <quic_c_gdjako@quicinc.com>
In-Reply-To: <833493d2-d585-47ee-c258-79eae5deff36@redhat.com>
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On 9/27/2021 6:51 PM, David Hildenbrand wrote:
> On 24.09.21 00:54, Chris Goldsworthy wrote:
>> From: Sudarshan Rajagopalan <quic_sudaraja@quicinc.com>
>>
>> After new memory blocks have been hotplugged, max_pfn and max_low_pfn
>> needs updating to reflect on new PFNs being hot added to system.
>>
>> Signed-off-by: Sudarshan Rajagopalan <quic_sudaraja@quicinc.com>
>> Signed-off-by: Chris Goldsworthy <quic_cgoldswo@quicinc.com>
>> ---
>>   arch/arm64/mm/mmu.c | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index cfd9deb..fd85b51 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -1499,6 +1499,11 @@ int arch_add_memory(int nid, u64 start, u64 size,
>>       if (ret)
>>           __remove_pgd_mapping(swapper_pg_dir,
>>                        __phys_to_virt(start), size);
>> +    else {
>> +        max_pfn = PFN_UP(start + size);
>> +        max_low_pfn = max_pfn;
>> +    }
>> +
>>       return ret;
> 
> Note: didn't verify if updating max_low_pfn is correct here.

My understanding is that max_low_pfn defines the low/high memory
boundary and it should be also updated.

Thanks,
Georgi