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SubjectRe: [PATCH 2/4] reduce stack usage in kvm_vcpu_ioctl()
Dave Hansen wrote:
> Same as the last one, but this time we use kmalloc()
> for all of the uses.
>
> Note that the kfree()s take advantage of the fact that
> kfree() is OK on NULL.
>
> Signed-off-by: Dave Hansen <dave@linux.vnet.ibm.com>
> ---
> virt/kvm/kvm_main.c | 48 ++++++++++++++++++++++++++++++------------------
> 1 files changed, 30 insertions(+), 18 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 7dd9b0b..70bf180 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1118,6 +1118,9 @@ static long kvm_vcpu_ioctl(struct file *filp,
> struct kvm_vcpu *vcpu = filp->private_data;
> void __user *argp = (void __user *)arg;
> int r;
> + struct kvm_fpu *fpu = NULL;
> + struct kvm_sregs *kvm_sregs = NULL;
> +
>

Spurious blank line.

>
> if (vcpu->kvm->mm != current->mm)
> return -EIO;
> @@ -1165,25 +1168,29 @@ out_free2:
> break;
> }
> case KVM_GET_SREGS: {
> - struct kvm_sregs kvm_sregs;
> -
> - memset(&kvm_sregs, 0, sizeof kvm_sregs);
> - r = kvm_arch_vcpu_ioctl_get_sregs(vcpu, &kvm_sregs);
> + kvm_sregs = kzalloc(sizeof(struct kvm_sregs), GFP_KERNEL);
> + r = -ENOMEM;
> + if (!kvm_sregs)
> + goto out;
> + memset(kvm_sregs, 0, sizeof(struct kvm_sregs));
>

memset unneeded after kzalloc.


btw, this is a generic problem, and could be handled generically:

struct ioctl_handler_entry {
u32 ioctl;
union {
long (*handler_parg)(void *arg);
long (*handler_larg)(long arg);
};
};

void process_ioctl(struct ioctl_handler_entry *ioctls)
{
search for correct entry;
allocate memory (get size from ioctl number);
copy from user (if _IOW);
call handler;
copy to user (if _IOR, and no error);
free memory;
}

I imagine this can be used to simplify many ioctls.

--
error compiling committee.c: too many arguments to function



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