linux-kernel - Re: [PATCH v12 7/7] x86/crash: Add x86 crash hotplug support

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Message-ID: <c83da0ea-8b1a-ffab-6968-acb2e488ff59@oracle.com>
Date:   Wed, 12 Oct 2022 11:23:37 -0500
From:   Eric DeVolder <eric.devolder@...cle.com>
To:     Sourabh Jain <sourabhjain@...ux.ibm.com>,
        Borislav Petkov <bp@...en8.de>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        kexec@...ts.infradead.org, ebiederm@...ssion.com,
        dyoung@...hat.com, bhe@...hat.com, vgoyal@...hat.com,
        tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
        hpa@...or.com, nramas@...ux.microsoft.com, thomas.lendacky@....com,
        robh@...nel.org, efault@....de, rppt@...nel.org, david@...hat.com,
        konrad.wilk@...cle.com, boris.ostrovsky@...cle.com
Subject: Re: [PATCH v12 7/7] x86/crash: Add x86 crash hotplug support



On 10/11/22 23:55, Sourabh Jain wrote:
> 
>>>>>> If kmap_local_page() works for all archs, then I'm happy to drop these
>>>>>> arch_ variants and use it directly.
>>>>>
>>>>> Yes, pls do.
>>>>
>>>> I'll check with Sourabh to see if PPC can work with kmap_local_page().
>>> I think kmap_local_page do support on  PowerPC. But can you explain why we need this
>>> function here, aren't the reserve memory already available to use?
>>
>> On x86, attempts to access the elfcorehdr without mapping it did not work (resulted
>> in a fault).
>>
>> Let me know if using kmap_local_page() in place of __va() in arch_map_crash_pages().
>> If it does, then I can eliminate arch_un/map_crash_pages() and use kmap_local_page()
>> directly.
> Hello Eric,
> 
> Atleast on ppc64 we have direct mapping available and hence just by doing page shift
> on physical address (__va) we can get valid virtual address on powerpc. In short we don't
> have to generate mapping again to access reserved region.
> 
> Regardless let's go with kdump_local_page API, it is supported on powerpc.
> 
> Thanks,
> Sourabh Jain

Ok, I will go that route.
Thanks!
eric