On Mon, 2 Jul 2018 14:52:43 +1000 David Gibson <da...@gibson.dropbear.id.au> wrote:
> On Mon, Jul 02, 2018 at 02:33:30PM +1000, Alexey Kardashevskiy wrote: > > On Mon, 2 Jul 2018 14:08:52 +1000 > > David Gibson <da...@gibson.dropbear.id.au> wrote: > > > > > On Fri, Jun 29, 2018 at 05:07:47PM +1000, Alexey Kardashevskiy wrote: > > > > On Fri, 29 Jun 2018 15:18:20 +1000 > > > > Alexey Kardashevskiy <a...@ozlabs.ru> wrote: > > > > > > > > > On Fri, 29 Jun 2018 14:57:02 +1000 > > > > > David Gibson <da...@gibson.dropbear.id.au> wrote: > > > > > > > > > > > On Fri, Jun 29, 2018 at 02:51:21PM +1000, Alexey Kardashevskiy > > > > > > wrote: > > > > > > > On Fri, 29 Jun 2018 14:12:41 +1000 > > > > > > > David Gibson <da...@gibson.dropbear.id.au> wrote: > > > > > > > > > > > > > > > On Tue, Jun 26, 2018 at 03:59:26PM +1000, Alexey Kardashevskiy > > > > > > > > wrote: > > > > > > > > > We already have a check in > > > > > > > > > drivers/vfio/vfio_iommu_spapr_tce.c that > > > > > > > > > an IOMMU page is contained in the physical page so the PCI > > > > > > > > > hardware won't > > > > > > > > > get access to unassigned host memory. > > > > > > > > > > > > > > > > > > However we do not have this check in KVM fastpath (H_PUT_TCE > > > > > > > > > accelerated > > > > > > > > > code) so the user space can pin memory backed with 64k pages > > > > > > > > > and create > > > > > > > > > a hardware TCE table with a bigger page size. We were lucky > > > > > > > > > so far and > > > > > > > > > did not hit this yet as the very first time the mapping > > > > > > > > > happens > > > > > > > > > we do not have tbl::it_userspace allocated yet and fall back > > > > > > > > > to > > > > > > > > > the userspace which in turn calls VFIO IOMMU driver and that > > > > > > > > > fails > > > > > > > > > because of the check in vfio_iommu_spapr_tce.c which is really > > > > > > > > > sustainable solution. > > > > > > > > > > > > > > > > > > This stores the smallest preregistered page size in the > > > > > > > > > preregistered > > > > > > > > > region descriptor and changes the mm_iommu_xxx API to check > > > > > > > > > this against > > > > > > > > > the IOMMU page size. > > > > > > > > > > > > > > > > > > Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru> > > > > > > > > > --- > > > > > > > > > Changes: > > > > > > > > > v2: > > > > > > > > > * explicitly check for compound pages before calling > > > > > > > > > compound_order() > > > > > > > > > > > > > > > > > > --- > > > > > > > > > The bug is: run QEMU _without_ hugepages (no -mempath) and > > > > > > > > > tell it to > > > > > > > > > advertise 16MB pages to the guest; a typical pseries guest > > > > > > > > > will use 16MB > > > > > > > > > for IOMMU pages without checking the mmu pagesize and this > > > > > > > > > will fail > > > > > > > > > at > > > > > > > > > https://git.qemu.org/?p=qemu.git;a=blob;f=hw/vfio/common.c;h=fb396cf00ac40eb35967a04c9cc798ca896eed57;hb=refs/heads/master#l256 > > > > > > > > > > > > > > > > > > With the change, mapping will fail in KVM and the guest will > > > > > > > > > print: > > > > > > > > > > > > > > > > > > mlx5_core 0000:00:00.0: ibm,create-pe-dma-window(2027) 0 > > > > > > > > > 8000000 20000000 18 1f returned 0 (liobn = 0x80000001 > > > > > > > > > starting addr = 8000000 0) > > > > > > > > > mlx5_core 0000:00:00.0: created tce table LIOBN 0x80000001 > > > > > > > > > for /pci@800000020000000/ethernet@0 > > > > > > > > > mlx5_core 0000:00:00.0: failed to map direct window for > > > > > > > > > /pci@800000020000000/ethernet@0: -1 > > > > > > > > > > > > > > > > [snip] > > > > > > > > > @@ -124,7 +125,7 @@ long mm_iommu_get(struct mm_struct *mm, > > > > > > > > > unsigned long ua, unsigned long entries, > > > > > > > > > struct mm_iommu_table_group_mem_t **pmem) > > > > > > > > > { > > > > > > > > > struct mm_iommu_table_group_mem_t *mem; > > > > > > > > > - long i, j, ret = 0, locked_entries = 0; > > > > > > > > > + long i, j, ret = 0, locked_entries = 0, pageshift; > > > > > > > > > struct page *page = NULL; > > > > > > > > > > > > > > > > > > mutex_lock(&mem_list_mutex); > > > > > > > > > @@ -166,6 +167,8 @@ long mm_iommu_get(struct mm_struct *mm, > > > > > > > > > unsigned long ua, unsigned long entries, > > > > > > > > > goto unlock_exit; > > > > > > > > > } > > > > > > > > > > > > > > > > > > + mem->pageshift = 30; /* start from 1G pages - the > > > > > > > biggest we have */ > > > > > > > > > > > > > > > > What about 16G pages on an HPT system? > > > > > > > > > > > > > > > > > > > > > Below in the loop mem->pageshift will reduce to the biggest > > > > > > > actual size > > > > > > > which will be 16mb/64k/4k. Or remain 1GB if no memory is actually > > > > > > > pinned, no loss there. > > > > > > > > > > > > Are you saying that 16G IOMMU pages aren't supported? Or that > > > > > > there's > > > > > > some reason a guest can never use them? > > > > > > > > > > > > > > > ah, 16_G_, not _M_. My bad. I just never tried such huge pages, I will > > > > > lift the limit up to 64 then, easier this way. > > > > > > > > > > > > Ah, no, rather this as the upper limit: > > > > > > > > mem->pageshift = ilog2(entries) + PAGE_SHIFT; > > > > > > I can't make sense of this comment in context. I see how you're > > > computing the minimum page size in the reserved region. > > > > > > My question is about what the is - the starting > > > value from which you calculate. Currently it's 1G, but I can't > > > immediately see a reason that 16G is impossible here. > > > > > > 16GB is impossible if the chunk we are preregistering here is smaller > > than that, for example, the entire guest ram is 4GB. > > Of course. Just like it was for 1GiB if you had a 512MiB guest, for > example. I'm talking about a case where you have a guest that's > >=16GiB and you *have* allocated 16GiB hugepages to back it. Then, assuming we are preregistering entire RAM as a single chunk, the "maximum minimum" will be initialized as ">=16GiB" (but floor-aligned to power of two) before the pinning loop and then reduce to the actual page size, inside the loop. I feel like I am missing something in the question, what is that? -- Alexey
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