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Subject: Re: [PATCH v2 2/2] KVM: PPC: Book3S HV: rework secure mem slot
 dropping
To:     Ram Pai <linuxram@us.ibm.com>, paulus@samba.org
Cc:     linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        kvm-ppc@vger.kernel.org, mpe@ellerman.id.au, sukadev@linux.ibm.com,
        bauerman@linux.ibm.com, bharata@linux.ibm.com,
        Paul Mackerras <paulus@ozlabs.org>
References: <20200721104202.15727-1-ldufour@linux.ibm.com>
 <20200721104202.15727-3-ldufour@linux.ibm.com>
 <20200721213736.GG7339@oc0525413822.ibm.com>
From:   Laurent Dufour <ldufour@linux.ibm.com>
Message-ID: <9158d2d7-7446-6eaa-8c88-666264c53dda@linux.ibm.com>
Date:   Wed, 22 Jul 2020 09:18:20 +0200
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Le 21/07/2020 à 23:37, Ram Pai a écrit :
> On Tue, Jul 21, 2020 at 12:42:02PM +0200, Laurent Dufour wrote:
>> When a secure memslot is dropped, all the pages backed in the secure device
>> (aka really backed by secure memory by the Ultravisor) should be paged out
>> to a normal page. Previously, this was achieved by triggering the page
>> fault mechanism which is calling kvmppc_svm_page_out() on each pages.
>>
>> This can't work when hot unplugging a memory slot because the memory slot
>> is flagged as invalid and gfn_to_pfn() is then not trying to access the
>> page, so the page fault mechanism is not triggered.
>>
>> Since the final goal is to make a call to kvmppc_svm_page_out() it seems
>> simpler to directly calling it instead of triggering such a mechanism. This
>              ^^ call directly instead of triggering..
> 
>> way kvmppc_uvmem_drop_pages() can be called even when hot unplugging a
>> memslot.
>>
>> Since kvmppc_uvmem_drop_pages() is already holding kvm->arch.uvmem_lock,
>> the call to __kvmppc_svm_page_out() is made.
>> As __kvmppc_svm_page_out needs the vma pointer to migrate the pages, the
>> VMA is fetched in a lazy way, to not trigger find_vma() all the time. In
>> addition, the mmap_sem is help in read mode during that time, not in write
> 		          ^^ held
> 
>> mode since the virual memory layout is not impacted, and
>> kvm->arch.uvmem_lock prevents concurrent operation on the secure device.
>>
>> Cc: Ram Pai <linuxram@us.ibm.com>
> 
> Reviewed-by: Ram Pai <linuxram@us.ibm.com>

Thanks for reviewing this series.

Regarding the wordsmithing, Paul, could you manage that when pulling the series?

Thanks,
Laurent.