On 07.11.19 19:22, David Hildenbrand wrote:
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.
I just realized the "boot memory" part. Is that a real thing? IOW, can
we have ZONE_DEVICE falling into a memory block (with holes)? I somewhat
have doubts that this would work ...
--
Thanks,
David / dhildenb
