On 06/11/17 21:45, Michael Ellerman wrote: > 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?
Yes, as Jonas already said. > If > so I guess the only concern is that this code might be called via some > other path that doesn't do that check. It is also called from pnv_pci_ioda2_setup_default_config() to create a 32bit DMA window which is limited by __rounddown_pow_of_two(memory_hotplug_max()). I'll repost. Thanks. -- Alexey
