Re: [patch] kvm: suppress KVM_SET_GSI_ROUTING allocation failure

[Paolo Bonzini]

On 08/02/2018 22:35, David Rientjes wrote:
> The KVM_SET_GSI_ROUTING ioctl does a vmalloc() of
> sizeof(struct kvm_irq_routing_entry) multiplied by a user-supplied value.
> This can be up to 4096 entries on architectures such as arm64 and s390
> (and the upper bound may be increased on s390 eventually).
> 
> This can produce a vmalloc allocation failure warning:
> 
> vmalloc: allocation failure: 0 bytes, mode:0x24000c2(GFP_KERNEL|__GFP_HIGHMEM)
> Call Trace:
>  __dump_stack lib/dump_stack.c:15 [inline]
>  dump_stack+0xf6/0x184 lib/dump_stack.c:51
>  warn_alloc+0x208/0x230 mm/page_alloc.c:2930
>  __vmalloc_node_range_memcg+0x510/0x670 mm/vmalloc.c:1711
>  __vmalloc_node_memcg mm/vmalloc.c:1751 [inline]
>  __vmalloc_node_memcg_flags mm/vmalloc.c:1788 [inline]
>  vmalloc+0x69/0x70 mm/vmalloc.c:1803
>  kvm_vm_ioctl+0x910/0x15e0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:4153
>  vfs_ioctl fs/ioctl.c:44 [inline]
>  do_vfs_ioctl+0x842/0xee0 fs/ioctl.c:611
>  SYSC_ioctl fs/ioctl.c:626 [inline]
>  SyS_ioctl+0x94/0xc0 fs/ioctl.c:617
>  entry_SYSCALL_64_fastpath+0x12/0x17
> 
> If the vmalloc address space is fully depleted, the ioctl can gracefully
> fail.  Add __GFP_NOWARN to the allocation to suppress the warning.
> 
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>

Queued, thanks.

Paolo

> ---
>  virt/kvm/kvm_main.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 001085b611ad..d0352dd45b95 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -3063,7 +3063,8 @@ static long kvm_vm_ioctl(struct file *filp,
>  			goto out;
>  		if (routing.nr) {
>  			r = -ENOMEM;
> -			entries = vmalloc(routing.nr * sizeof(*entries));
> +			entries = __vmalloc(routing.nr * sizeof(*entries),
> +					GFP_KERNEL | __GFP_NOWARN, PAGE_KERNEL);
>  			if (!entries)
>  				goto out;
>  			r = -EFAULT;
>