On Wed, Feb 27, 2013 at 11:56:55AM +1030, Rusty Russell wrote: > Aurelien Jarno <aurelien@xxxxxxxxxxx> writes: > > Hi, > > > > I have noticed that virtio-rng only returns zero for kernels >= 2.6.33 > > built with CONFIG_HW_RANDOM=m. This is a bit much too predictable for a > > random generator ;-). > > > > The reason for that is virtio expects guest real addresses, while > > rng_core.ko (ie when built as a module) is passing a vmalloced buffer > > to the virtio-rng read function, declared as such: > > > > static u8 rng_buffer[SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES] > > __cacheline_aligned; > > > > This is basically the same issue than the following one: > > > > https://lists.linux-foundation.org/pipermail/virtualization/2008-May/010946.html > > > > but introduced in a more subtle way in this commit: > > > > commit bb347d98079a547e80bd4722dee1de61e4dca0e8 > > Author: Ian Molton <ian.molton@xxxxxxxxxxxxxxx> > > Date: Tue Dec 1 15:26:33 2009 +0800 > > OK, I looked at doing a kmalloc and copy in virtio_rng, but it's very > inelegant (we don't know what size of buffer to allocate). On the other hand, the rng API allows to return less bytes than requested, so it's possible to have a fixed buffer size of for example 64 or 128 bytes. But I agree it's better to do that in rng core. > No driver other than virtio_rng cares about this issue, but it's still > far easier to fix in the core. > > How's this? Works here... > > Subject: hw_random: make buffer usable in scatterlist. > > virtio_rng feeds the randomness buffer handed by the core directly > into the scatterlist, since commit bb347d98079a547e80bd4722dee1de61e4dca0e8. > > However, if CONFIG_HW_RANDOM=m, the static buffer isn't a linear address > (at least on most archs). We could fix this in virtio_rng, but it's actually > far easier to just do it in the core as virtio_rng would have to allocate > a buffer every time (it doesn't know how much the core will want to read). > > Reported-by: Aurelien Jarno <aurelien@xxxxxxxxxxx> > Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx> > > diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c > index 1bafb40..69ae597 100644 > --- a/drivers/char/hw_random/core.c > +++ b/drivers/char/hw_random/core.c > @@ -40,6 +40,7 @@ > #include <linux/init.h> > #include <linux/miscdevice.h> > #include <linux/delay.h> > +#include <linux/slab.h> > #include <asm/uaccess.h> > > > @@ -52,8 +53,12 @@ static struct hwrng *current_rng; > static LIST_HEAD(rng_list); > static DEFINE_MUTEX(rng_mutex); > static int data_avail; > -static u8 rng_buffer[SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES] > - __cacheline_aligned; > +static u8 *rng_buffer; > + > +static size_t rng_buffer_size(void) > +{ > + return SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES; > +} > > static inline int hwrng_init(struct hwrng *rng) > { > @@ -116,7 +121,7 @@ static ssize_t rng_dev_read(struct file *filp, char __user *buf, > > if (!data_avail) { > bytes_read = rng_get_data(current_rng, rng_buffer, > - sizeof(rng_buffer), > + rng_buffer_size(), > !(filp->f_flags & O_NONBLOCK)); > if (bytes_read < 0) { > err = bytes_read; > @@ -307,6 +312,14 @@ int hwrng_register(struct hwrng *rng) > > mutex_lock(&rng_mutex); > > + /* kmalloc makes this safe for virt_to_page() in virtio_rng.c */ > + err = -ENOMEM; > + if (!rng_buffer) { > + rng_buffer = kmalloc(rng_buffer_size(), GFP_KERNEL); > + if (!rng_buffer) > + goto out_unlock; > + } > + > /* Must not register two RNGs with the same name. */ > err = -EEXIST; > list_for_each_entry(tmp, &rng_list, list) { > It works fine for me. Thanks for the patch. Tested-by: Aurelien Jarno <aurelien@xxxxxxxxxxx> -- Aurelien Jarno GPG: 1024D/F1BCDB73 aurelien@xxxxxxxxxxx http://www.aurel32.net -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
