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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Laurent Dufour <ldufour@linux.ibm.com>, bharata@linux.ibm.com
Cc:     linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, paulus@samba.org,
        bauerman@linux.ibm.com, sukadev@linux.ibm.com,
        sathnaga@linux.vnet.ibm.com, Ram Pai <linuxram@us.ibm.com>,
        Paul Mackerras <paulus@ozlabs.org>
Subject: Re: [PATCH 2/2] KVM: PPC: Book3S HV: rework secure mem slot dropping
In-Reply-To: <0588d16a-8548-0f55-1132-400807a390a1@linux.ibm.com>
References: <20200703155914.40262-1-ldufour@linux.ibm.com> <20200703155914.40262-3-ldufour@linux.ibm.com> <20200708112531.GA7902@in.ibm.com> <0588d16a-8548-0f55-1132-400807a390a1@linux.ibm.com>
Date:   Thu, 09 Jul 2020 21:13:11 +1000
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Laurent Dufour <ldufour@linux.ibm.com> writes:
> Le 08/07/2020 =C3=A0 13:25, Bharata B Rao a =C3=A9crit=C2=A0:
>> On Fri, Jul 03, 2020 at 05:59:14PM +0200, Laurent Dufour wrote:
>>> When a secure memslot is dropped, all the pages backed in the secure de=
vice
>>> (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 sl=
ot
>>> 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
>>> way kvmppc_uvmem_drop_pages() can be called even when hot unplugging a
>>> memslot.
>>=20
>> Yes, this appears much simpler.
>
> Thanks Bharata for reviewing this.
>
>>=20
>>>
>>> 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 wr=
ite
>>> 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: Laurent Dufour <ldufour@linux.ibm.com>
>>> ---
>>>   arch/powerpc/kvm/book3s_hv_uvmem.c | 54 ++++++++++++++++++++----------
>>>   1 file changed, 37 insertions(+), 17 deletions(-)
>>>
>>> diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book=
3s_hv_uvmem.c
>>> index 852cc9ae6a0b..479ddf16d18c 100644
>>> --- a/arch/powerpc/kvm/book3s_hv_uvmem.c
>>> +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
>>> @@ -533,35 +533,55 @@ static inline int kvmppc_svm_page_out(struct vm_a=
rea_struct *vma,
>>>    * fault on them, do fault time migration to replace the device PTEs =
in
>>>    * QEMU page table with normal PTEs from newly allocated pages.
>>>    */
>>> -void kvmppc_uvmem_drop_pages(const struct kvm_memory_slot *free,
>>> +void kvmppc_uvmem_drop_pages(const struct kvm_memory_slot *slot,
>>>   			     struct kvm *kvm, bool skip_page_out)
>>>   {
>>>   	int i;
>>>   	struct kvmppc_uvmem_page_pvt *pvt;
>>> -	unsigned long pfn, uvmem_pfn;
>>> -	unsigned long gfn =3D free->base_gfn;
>>> +	struct page *uvmem_page;
>>> +	struct vm_area_struct *vma =3D NULL;
>>> +	unsigned long uvmem_pfn, gfn;
>>> +	unsigned long addr, end;
>>> +
>>> +	down_read(&kvm->mm->mmap_sem);
>>=20
>> You should be using mmap_read_lock(kvm->mm) with recent kernels.
>
> Absolutely, shame on me, I reviewed Michel's series about that!
>
> Paul, Michael, could you fix that when pulling this patch or should I sen=
t a=20
> whole new series?

Paul will take this series, so up to him.

cheers