On 2021/4/22 16:00, Santosh Shukla wrote: > On Thu, Apr 22, 2021 at 1:07 PM Tarun Gupta (SW-GPU) > <targupta@xxxxxxxxxx> wrote: >> >> >> >> On 4/22/2021 12:20 PM, Marc Zyngier wrote: >>> External email: Use caution opening links or attachments >>> >>> >>> On Thu, 22 Apr 2021 03:02:00 +0100, >>> Gavin Shan <gshan@xxxxxxxxxx> wrote: >>>> >>>> Hi Marc, >>>> >>>> On 4/21/21 9:59 PM, Marc Zyngier wrote: >>>>> On Wed, 21 Apr 2021 07:17:44 +0100, >>>>> Keqian Zhu <zhukeqian1@xxxxxxxxxx> wrote: >>>>>> On 2021/4/21 14:20, Gavin Shan wrote: >>>>>>> On 4/21/21 12:59 PM, Keqian Zhu wrote: >>>>>>>> On 2020/10/22 0:16, Santosh Shukla wrote: >>>>>>>>> The Commit:6d674e28 introduces a notion to detect and handle the >>>>>>>>> device mapping. The commit checks for the VM_PFNMAP flag is set >>>>>>>>> in vma->flags and if set then marks force_pte to true such that >>>>>>>>> if force_pte is true then ignore the THP function check >>>>>>>>> (/transparent_hugepage_adjust()). >>>>>>>>> >>>>>>>>> There could be an issue with the VM_PFNMAP flag setting and checking. >>>>>>>>> For example consider a case where the mdev vendor driver register's >>>>>>>>> the vma_fault handler named vma_mmio_fault(), which maps the >>>>>>>>> host MMIO region in-turn calls remap_pfn_range() and maps >>>>>>>>> the MMIO's vma space. Where, remap_pfn_range implicitly sets >>>>>>>>> the VM_PFNMAP flag into vma->flags. >>>>>>>> Could you give the name of the mdev vendor driver that triggers this issue? >>>>>>>> I failed to find one according to your description. Thanks. >>>>>>>> >>>>>>> >>>>>>> I think it would be fixed in driver side to set VM_PFNMAP in >>>>>>> its mmap() callback (call_mmap()), like vfio PCI driver does. >>>>>>> It means it won't be delayed until page fault is issued and >>>>>>> remap_pfn_range() is called. It's determined from the beginning >>>>>>> that the vma associated the mdev vendor driver is serving as >>>>>>> PFN remapping purpose. So the vma should be populated completely, >>>>>>> including the VM_PFNMAP flag before it becomes visible to user >>>>>>> space. >>>>> >>>>> Why should that be a requirement? Lazy populating of the VMA should be >>>>> perfectly acceptable if the fault can only happen on the CPU side. >>>>> > > Right. > Hi keqian, > You can refer to case > http://lkml.iu.edu/hypermail/linux/kernel/2010.3/00952.html Hi Santosh, Yeah, thanks for that. BRs, Keqian
