On Tue, 2012-03-27 at 17:00 -0400, Jason Baron wrote:
> The current 'kvm_init_irq_routing()' doesn't set up the gsi bitmap
> correctly, and as a consequence pins max_gsi to 32 when it really
> should be 1024. I ran into this limitation while testing pci
> passthrough, where I consistently would get -ENOSPACE return from
> kvm_get_irq_route_gsi() in assigned_dev_update_msix_mmio().
>
> Signed-off-by: Jason Baron <jbaron@xxxxxxxxxx>
> ---
> kvm-all.c | 4 ++--
> qemu-kvm.c | 2 +-
> 2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kvm-all.c b/kvm-all.c
> index ab88c7c..7d602af 100644
> --- a/kvm-all.c
> +++ b/kvm-all.c
> @@ -873,9 +873,9 @@ static void kvm_init_irq_routing(KVMState *s)
> unsigned int gsi_bits, i;
>
> /* Round up so we can search ints using ffs */
> - gsi_bits = (gsi_count + 31) / 32;
> + gsi_bits = ALIGN(gsi_count, 32);
> s->used_gsi_bitmap = g_malloc0(gsi_bits / 8);
I think the above is all that's needed (it actually used to be this,
then got broken in 84b058d). But if we do this:
> - s->max_gsi = gsi_bits;
> + s->max_gsi = gsi_count;
Then we'll hit this assert from the code immediately below where we're
marking over-allocated bits as already used if we actually did a
round-up:
static void set_gsi(KVMState *s, unsigned int gsi)
{
assert(gsi < s->max_gsi);
Sorry, I had forgotten about this pre-allocation trick to avoid
returning > gsi_count when we talked about this.
>
> /* Mark any over-allocated bits as already in use */
> for (i = gsi_count; i < gsi_bits; i++) {
> diff --git a/qemu-kvm.c b/qemu-kvm.c
> index 2047ebb..b17cae0 100644
> --- a/qemu-kvm.c
> +++ b/qemu-kvm.c
> @@ -249,7 +249,7 @@ int kvm_get_irq_route_gsi(void)
> uint32_t *buf = s->used_gsi_bitmap;
>
> /* Return the lowest unused GSI in the bitmap */
And we get to avoid doing this ALIGN on every search.
> - for (i = 0; i < s->max_gsi / 32; i++) {
> + for (i = 0; i < (ALIGN(s->max_gsi, 32) / 32); i++) {
> bit = ffs(~buf[i]);
> if (!bit) {
> continue;
Thanks,
Alex
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