On 04/19/2018 08:29 PM, Marc Orr wrote:
> The kvm struct is (currently) tens of kilo-bytes, which turns out to be a
> large amount of memory to allocate contiguously via kzalloc. Thus, this
> patch changes the kzalloc to a vzalloc, so that the memory allocation is
> less likely to fail in resource-constrained environments.
>
> Signed-off-by: Marc Orr <marcorr@xxxxxxxxxx>
> ---
> include/linux/kvm_host.h | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 6930c63126c7..cf7b6a3a4197 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -19,6 +19,7 @@
> #include <linux/preempt.h>
> #include <linux/msi.h>
> #include <linux/slab.h>
> +#include <linux/vmalloc.h>
> #include <linux/rcupdate.h>
> #include <linux/ratelimit.h>
> #include <linux/err.h>
> @@ -810,12 +811,12 @@ int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu);
> #ifndef __KVM_HAVE_ARCH_VM_ALLOC
> static inline struct kvm *kvm_arch_alloc_vm(void)
> {
> - return kzalloc(sizeof(struct kvm), GFP_KERNEL);
> + return vzalloc(sizeof(struct kvm));
> }
>
> static inline void kvm_arch_free_vm(struct kvm *kvm)
> {
> - kfree(kvm);
> + vfree(kvm);
> }
> #endif
>
I dont think this is necessarily safe. This contains kvm_arch and you
would need to verify that no architecture has data in struct kvm_arch
that must be allocated with kmalloc. Fo example on s390 kernel virtual
== kernel real for kmalloc so some driver might rely on that.
FWIW, it looks like the s390 struct kvm_arch is fine, but this requires
more review I guess.
Another thing:
In s390 this is 14760 bytes and on x86 it seems to be 12440 on my system.
This should never fail, no?
