linux-kernel - Re: [patch] kvm: suppress KVM_SET_GSI

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Date:   Tue, 13 Feb 2018 15:48:36 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [patch] kvm: suppress KVM_SET_GSI_ROUTING allocation failure

On Thu 08-02-18 13:35:08, 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)

I am not arguing about the kvm change but do we actaully want to warn
for 0 sized allocations? This just doesn't make much sense to me.
In other words don't we want this?

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 673942094328..c5d832510c54 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1748,7 +1748,9 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
 	unsigned long real_size = size;
 
 	size = PAGE_ALIGN(size);
-	if (!size || (size >> PAGE_SHIFT) > totalram_pages)
+	if (!size)
+		return NULL;
+	if ((size >> PAGE_SHIFT) > totalram_pages)
 		goto fail;
 
 	area = __get_vm_area_node(size, align, VM_ALLOC | VM_UNINITIALIZED |
-- 
Michal Hocko
SUSE Labs