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Date: Mon, 27 Jul 2020 09:19:05 +0530
From: Bharata B Rao <bharata@linux.ibm.com>
To: Laurent Dufour <ldufour@linux.ibm.com>
Subject: Re: [PATCH] KVM: PPC: Book3S HV: rework secure mem slot dropping
Message-ID: <20200727034905.GF1082478@in.ibm.com>
References: <20200724030337.GC1082478@in.ibm.com>
 <20200724083527.28027-1-ldufour@linux.ibm.com>
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Cc: aneesh.kumar@linux.ibm.com, linuxram@us.ibm.com, cclaudio@linux.ibm.com,
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On Fri, Jul 24, 2020 at 10:35:27AM +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 call directly instead of triggering such a mechanism. This
> 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 held in read mode during
> that time, not in write 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>
> Cc: Bharata B Rao <bharata@linux.ibm.com>
> Cc: Paul Mackerras <paulus@ozlabs.org>
> Signed-off-by: Ram Pai <linuxram@us.ibm.com>
> 	[modified the changelog description]
> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
>         [modified check on the VMA in kvmppc_uvmem_drop_pages]

Reviewed-by: Bharata B Rao <bharata@linux.ibm.com>

Regards,
Bharata.

From mboxrd@z Thu Jan  1 00:00:00 1970
From: Bharata B Rao <bharata@linux.ibm.com>
Date: Mon, 27 Jul 2020 03:49:28 +0000
Subject: Re: [PATCH] KVM: PPC: Book3S HV: rework secure mem slot dropping
Message-Id: <20200727034905.GF1082478@in.ibm.com>
List-Id: <kvm-ppc.vger.kernel.org>
References: <20200724030337.GC1082478@in.ibm.com>
 <20200724083527.28027-1-ldufour@linux.ibm.com>
In-Reply-To: <20200724083527.28027-1-ldufour@linux.ibm.com>
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To: Laurent Dufour <ldufour@linux.ibm.com>
Cc: aneesh.kumar@linux.ibm.com, linuxram@us.ibm.com, cclaudio@linux.ibm.com, kvm-ppc@vger.kernel.org, sathnaga@linux.vnet.ibm.com, sukadev@linux.ibm.com, linuxppc-dev@lists.ozlabs.org, bauerman@linux.ibm.com, david@gibson.dropbear.id.au

On Fri, Jul 24, 2020 at 10:35:27AM +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 call directly instead of triggering such a mechanism. This
> 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 held in read mode during
> that time, not in write 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>
> Cc: Bharata B Rao <bharata@linux.ibm.com>
> Cc: Paul Mackerras <paulus@ozlabs.org>
> Signed-off-by: Ram Pai <linuxram@us.ibm.com>
> 	[modified the changelog description]
> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
>         [modified check on the VMA in kvmppc_uvmem_drop_pages]

Reviewed-by: Bharata B Rao <bharata@linux.ibm.com>

Regards,
Bharata.