From: Laurent Dufour <ldufour@linux.ibm.com>
To: bharata@linux.ibm.com, linuxram@us.ibm.com
Cc: linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org,
paulus@samba.org, sukadev@linux.ibm.com,
linuxppc-dev@lists.ozlabs.org, bauerman@linux.ibm.com
Subject: Re: [PATCH v2 2/2] KVM: PPC: Book3S HV: rework secure mem slot dropping
Date: Thu, 23 Jul 2020 14:32:30 +0200 [thread overview]
Message-ID: <4a3caeaf-cd0c-fcd7-0a97-f367a5f78dac@linux.ibm.com> (raw)
In-Reply-To: <20200723033600.GS7902@in.ibm.com>
Le 23/07/2020 à 05:36, Bharata B Rao 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
>> 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
>> 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/book3s_hv_uvmem.c
>> index 5a4b02d3f651..ba5c7c77cc3a 100644
>> --- a/arch/powerpc/kvm/book3s_hv_uvmem.c
>> +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
>> @@ -624,35 +624,55 @@ static inline int kvmppc_svm_page_out(struct vm_area_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 = free->base_gfn;
>> + struct page *uvmem_page;
>> + struct vm_area_struct *vma = NULL;
>> + unsigned long uvmem_pfn, gfn;
>> + unsigned long addr, end;
>> +
>> + mmap_read_lock(kvm->mm);
>> +
>> + addr = slot->userspace_addr;
>
> We typically use gfn_to_hva() for that, but that won't work for a
> memslot that is already marked INVALID which is the case here.
> I think it is ok to access slot->userspace_addr here of an INVALID
> memslot, but just thought of explictly bringing this up.
Which explicitly mentioned above in the patch's description:
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.
>
>> + end = addr + (slot->npages * PAGE_SIZE);
>>
>> - for (i = free->npages; i; --i, ++gfn) {
>> - struct page *uvmem_page;
>> + gfn = slot->base_gfn;
>> + for (i = slot->npages; i; --i, ++gfn, addr += PAGE_SIZE) {
>> +
>> + /* Fetch the VMA if addr is not in the latest fetched one */
>> + if (!vma || (addr < vma->vm_start || addr >= vma->vm_end)) {
>> + vma = find_vma_intersection(kvm->mm, addr, end);
>> + if (!vma ||
>> + vma->vm_start > addr || vma->vm_end < end) {
>> + pr_err("Can't find VMA for gfn:0x%lx\n", gfn);
>> + break;
>> + }
>> + }
>
> In Ram's series, kvmppc_memslot_page_merge() also walks the VMAs spanning
> the memslot, but it uses a different logic for the same. Why can't these
> two cases use the same method to walk the VMAs? Is there anything subtly
> different between the two cases?
This is probably doable. At the time I wrote that patch, the
kvmppc_memslot_page_merge() was not yet introduced AFAIR.
This being said, I'd help a lot to factorize that code... I let Ram dealing with
that ;)
Cheers,
Laurent.
next prev parent reply other threads:[~2020-07-23 12:37 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-21 10:42 [PATCH v2 0/2] Rework secure memslot dropping Laurent Dufour
2020-07-21 10:42 ` [PATCH v2 1/2] KVM: PPC: Book3S HV: move kvmppc_svm_page_out up Laurent Dufour
2020-07-21 21:28 ` Ram Pai
2020-07-21 10:42 ` [PATCH v2 2/2] KVM: PPC: Book3S HV: rework secure mem slot dropping Laurent Dufour
2020-07-21 21:37 ` Ram Pai
2020-07-22 7:18 ` Laurent Dufour
2020-07-23 3:36 ` Bharata B Rao
2020-07-23 12:32 ` Laurent Dufour [this message]
2020-07-23 14:06 ` Laurent Dufour
2020-07-27 19:24 [PATCH v2 0/2] Rework secure memslot dropping Ram Pai
2020-07-27 19:24 ` [PATCH v2 2/2] KVM: PPC: Book3S HV: rework secure mem slot dropping Ram Pai
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4a3caeaf-cd0c-fcd7-0a97-f367a5f78dac@linux.ibm.com \
--to=ldufour@linux.ibm.com \
--cc=bauerman@linux.ibm.com \
--cc=bharata@linux.ibm.com \
--cc=kvm-ppc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=linuxram@us.ibm.com \
--cc=paulus@samba.org \
--cc=sukadev@linux.ibm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).