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Re: [Xen-devel] [PATCH v1 04/10] vfio/type1: Prepare is_invalid_reserved_pfn() for PG_reserved changes
- To: Dan Williams <dan.j.williams@xxxxxxxxx>
- From: David Hildenbrand <dhildenb@xxxxxxxxxx>
- Date: Thu, 7 Nov 2019 13:22:12 -0500 (EST)
- Cc: linux-hyperv@xxxxxxxxxxxxxxx, Michal Hocko <mhocko@xxxxxxxx>, Radim Krčmář <rkrcmar@xxxxxxxxxx>, KVM list <kvm@xxxxxxxxxxxxxxx>, David Hildenbrand <david@xxxxxxxxxx>, KarimAllah Ahmed <karahmed@xxxxxxxxx>, Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, Alexander Duyck <alexander.duyck@xxxxxxxxx>, Michal Hocko <mhocko@xxxxxxxxxx>, Paul Mackerras <paulus@xxxxxxxxxx>, Linux MM <linux-mm@xxxxxxxxx>, Pavel Tatashin <pavel.tatashin@xxxxxxxxxxxxx>, Paul Mackerras <paulus@xxxxxxxxx>, Michael Ellerman <mpe@xxxxxxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Wanpeng Li <wanpengli@xxxxxxxxxxx>, Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>, "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Kees Cook <keescook@xxxxxxxxxxxx>, devel@xxxxxxxxxxxxxxxxxxxx, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>, "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx>, Joerg Roedel <joro@xxxxxxxxxx>, X86 ML <x86@xxxxxxxxxx>, YueHaibing <yuehaibing@xxxxxxxxxx>, "Matthew Wilcox \(Oracle\)" <willy@xxxxxxxxxxxxx>, Mike Rapoport <rppt@xxxxxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Vlastimil Babka <vbabka@xxxxxxx>, Anthony Yznaga <anthony.yznaga@xxxxxxxxxx>, Oscar Salvador <osalvador@xxxxxxx>, "Isaac J. Manjarres" <isaacm@xxxxxxxxxxxxxx>, Matt Sickler <Matt.Sickler@xxxxxxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Anshuman Khandual <anshuman.khandual@xxxxxxx>, Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>, Sasha Levin <sashal@xxxxxxxxxx>, kvm-ppc@xxxxxxxxxxxxxxx, Qian Cai <cai@xxxxxx>, Alex Williamson <alex.williamson@xxxxxxxxxx>, Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Nicholas Piggin <npiggin@xxxxxxxxx>, Andy Lutomirski <luto@xxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>, Allison Randal <allison@xxxxxxxxxxx>, Jim Mattson <jmattson@xxxxxxxxxx>, Christophe Leroy <christophe.leroy@xxxxxx>, Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>, Cornelia Huck <cohuck@xxxxxxxxxx>, Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Sean Christopherson <sean.j.christopherson@xxxxxxxxx>, Johannes Weiner <hannes@xxxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, linuxppc-dev <linuxppc-dev@xxxxxxxxxxxxxxxx>
- Delivery-date: Fri, 08 Nov 2019 05:16:52 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: +s2g58aTrOooMxUTMjHg25AUP3zIIA==
- Thread-topic: vfio/type1: Prepare is_invalid_reserved_pfn() for PG_reserved changes
> Am 07.11.2019 um 16:40 schrieb Dan Williams <dan.j.williams@xxxxxxxxx>:
>
> On Thu, Oct 24, 2019 at 5:12 AM David Hildenbrand <david@xxxxxxxxxx> 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 is_invalid_reserved_pfn() similar to kvm_is_reserved_pfn() to make
>> sure the function produces the same result once we stop setting ZONE_DEVICE
>> pages PG_reserved.
>>
>> Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>
>> Cc: Cornelia Huck <cohuck@xxxxxxxxxx>
>> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
>> ---
>> drivers/vfio/vfio_iommu_type1.c | 10 ++++++++--
>> 1 file changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c
>> b/drivers/vfio/vfio_iommu_type1.c
>> index 2ada8e6cdb88..f8ce8c408ba8 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -299,9 +299,15 @@ static int vfio_lock_acct(struct vfio_dma *dma, long
>> npage, bool async)
>> */
>> static bool is_invalid_reserved_pfn(unsigned long pfn)
>> {
>> - if (pfn_valid(pfn))
>> - return PageReserved(pfn_to_page(pfn));
>> + struct page *page = pfn_to_online_page(pfn);
>
> Ugh, I just realized this is not a safe conversion until
> pfn_to_online_page() is moved over to subsection granularity. As it
> stands it will return true for any ZONE_DEVICE pages that share a
> section with boot memory.
That should not happen right now and I commented back when you introduced
subsection support that I don’t want to have ZONE_DEVICE mixed with online
pages in a section. Having memory block devices that partially span ZONE_DEVICE
would be ... really weird. With something like pfn_active() - as discussed - we
could at least make this check work - but I am not sure if we really want to go
down that path. In the worst case, some MB of RAM are lost ... I guess this
needs more thought.
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