Alexey Kardashevskiy <a...@ozlabs.ru> writes: > On 31/10/17 15:04, Alexey Kardashevskiy wrote: >> DMA windows can only have a size of power of two on IODA2 hardware and >> using memory_hotplug_max() to determine the upper limit won't work >> correcly if it returns not power of two value. >> >> This relaxes the check by rounding up the value returned by >> memory_hotplug_max(). >> >> It is expected to impact DPDK on machines with non-power-of-two RAM size, >> mostly. KVM guests are less likely to be affected as usually guests get >> less than half of hosts RAM. > > > It was pointed out that this check is quite useless anyway as the vm_locked > memory limit should hit first, and if that is not set or the user got the > root privilege level, then there are easier ways to crash the host so I am > thinking of: > > > diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c > b/arch/powerpc/platforms/powernv/pci-ioda.c > index 269f119e4b3c..a47e4cf343b2 100644 > --- a/arch/powerpc/platforms/powernv/pci-ioda.c > +++ b/arch/powerpc/platforms/powernv/pci-ioda.c > @@ -2769,7 +2769,7 @@ static long pnv_pci_ioda2_table_alloc_pages(int nid, > __u64 bus_offset, > if (!levels || (levels > POWERNV_IOMMU_MAX_LEVELS)) > return -EINVAL; > > - if ((window_size > memory_hotplug_max()) || > !is_power_of_2(window_size)) > + if (!is_power_of_2(window_size)) > return -EINVAL; > > > > Makes sense?
Sounds reasonable. Execpt where is the vm_locked check? I think it's in the VFIO driver? If so I guess the only concern is that this code might be called via some other path that doesn't do that check. cheers
