On Fri, Dec 06, 2019 at 10:08:02AM +0800, Jia He wrote: > In kvm_arch_prepare_memory_region, arm kvm regards the memory region as > writable if the flag has no KVM_MEM_READONLY, and the vm is readonly if > !VM_WRITE. > > But there is common usage for setting kvm memory region as follows: > e.g. qemu side (see the PROT_NONE flag) > 1. mmap(NULL, size, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); > memory_region_init_ram_ptr() > 2. re mmap the above area with read/write authority. > > Such example is used in virtio-fs qemu codes which hasn't been upstreamed > [1]. But seems we can't forbid this example. > > Without this patch, it will cause an EPERM during kvm_set_memory_region() > and cause qemu boot crash. > > As told by Ard, "the underlying assumption is incorrect, i.e., that the > value of vm_flags at this point in time defines how the VMA is used > during its lifetime. There may be other cases where a VMA is created > with VM_READ vm_flags that are changed to VM_READ|VM_WRITE later, and > we are currently rejecting this use case as well." > > [1] https://gitlab.com/virtio-fs/qemu/blob/5a356e/hw/virtio/vhost-user-fs.c#L488 Reviewed-by: Christoffer Dall <christoffer.dall@xxxxxxx> > > Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> > Suggested-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> > Signed-off-by: Jia He <justin.he@xxxxxxx> > --- > virt/kvm/arm/mmu.c | 9 --------- > 1 file changed, 9 deletions(-) > > diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c > index 38b4c910b6c3..a48994af70b8 100644 > --- a/virt/kvm/arm/mmu.c > +++ b/virt/kvm/arm/mmu.c > @@ -2301,15 +2301,6 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, > if (!vma || vma->vm_start >= reg_end) > break; > > - /* > - * Mapping a read-only VMA is only allowed if the > - * memory region is configured as read-only. > - */ > - if (writable && !(vma->vm_flags & VM_WRITE)) { > - ret = -EPERM; > - break; > - } > - > /* > * Take the intersection of this VMA with the memory region > */ > -- > 2.17.1 > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
