[PATCH v1 03/10] KVM: Prepare kvm_is_reserved_pfn() for PG_reserved changes
david at redhat.com
Tue Nov 5 09:17:54 UTC 2019
On 05.11.19 05:38, Dan Williams wrote:
> On Thu, Oct 24, 2019 at 5:11 AM David Hildenbrand <david at redhat.com> wrote:
>> Right now, ZONE_DEVICE memory is always set PG_reserved. We want to
>> change that.
>> KVM has this weird use case that you can map anything from /dev/mem
>> into the guest. pfn_valid() is not a reliable check whether the memmap
>> was initialized and can be touched. pfn_to_online_page() makes sure
>> that we have an initialized memmap (and don't have ZONE_DEVICE memory).
>> Rewrite kvm_is_reserved_pfn() to make sure the function produces the
>> same result once we stop setting ZONE_DEVICE pages PG_reserved.
>> Cc: Paolo Bonzini <pbonzini at redhat.com>
>> Cc: "Radim Krčmář" <rkrcmar at redhat.com>
>> Cc: Michal Hocko <mhocko at kernel.org>
>> Cc: Dan Williams <dan.j.williams at intel.com>
>> Cc: KarimAllah Ahmed <karahmed at amazon.de>
>> Signed-off-by: David Hildenbrand <david at redhat.com>
>> virt/kvm/kvm_main.c | 10 ++++++++--
>> 1 file changed, 8 insertions(+), 2 deletions(-)
>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>> index e9eb666eb6e8..9d18cc67d124 100644
>> --- a/virt/kvm/kvm_main.c
>> +++ b/virt/kvm/kvm_main.c
>> @@ -151,9 +151,15 @@ __weak int kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm,
>> bool kvm_is_reserved_pfn(kvm_pfn_t pfn)
>> - if (pfn_valid(pfn))
>> - return PageReserved(pfn_to_page(pfn));
>> + struct page *page = pfn_to_online_page(pfn);
>> + /*
>> + * We treat any pages that are not online (not managed by the buddy)
>> + * as reserved - this includes ZONE_DEVICE pages and pages without
>> + * a memmap (e.g., mapped via /dev/mem).
>> + */
>> + if (page)
>> + return PageReserved(page);
>> return true;
> So after this all the pfn_valid() usage in kvm_main.c is replaced with
> pfn_to_online_page()? Looks correct to me.
> However, I'm worried that kvm is taking reference on ZONE_DEVICE pages
> through some other path resulting in this:
> I'll see if this patch set modulates or maintains that failure mode.
I'd assume that the behavior is unchanged. Ithink we get a reference to
these ZONE_DEVICE pages via __get_user_pages_fast() and friends in
hva_to_pfn_fast() and friends in virt/kvm/kvm_main.c
David / dhildenb
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