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SubjectRe: [PATCH bpf-next V2] xsk: allow remap of fill and/or completion rings
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On 3/21/23 12:13 PM, Magnus Karlsson wrote:
> On Mon, 20 Mar 2023 at 21:54, Nuno Gonçalves <nunog@fr24.com> wrote:
>>
>> The remap of fill and completion rings was frowned upon as they
>> control the usage of UMEM which does not support concurrent use.
>> At the same time this would disallow the remap of these rings
>> into another process.
>>
>> A possible use case is that the user wants to transfer the socket/
>> UMEM ownership to another process (via SYS_pidfd_getfd) and so
>> would need to also remap these rings.
>>
>> This will have no impact on current usages and just relaxes the
>> remap limitation.
>
> Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
>
>> Signed-off-by: Nuno Gonçalves <nunog@fr24.com>
>> ---
>> net/xdp/xsk.c | 9 ++++++---
>> 1 file changed, 6 insertions(+), 3 deletions(-)
>>
>> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
>> index 2ac58b282b5eb..e2571ec067526 100644
>> --- a/net/xdp/xsk.c
>> +++ b/net/xdp/xsk.c
>> @@ -1301,9 +1301,10 @@ static int xsk_mmap(struct file *file, struct socket *sock,
>> loff_t offset = (loff_t)vma->vm_pgoff << PAGE_SHIFT;
>> unsigned long size = vma->vm_end - vma->vm_start;
>> struct xdp_sock *xs = xdp_sk(sock->sk);
>> + int state = READ_ONCE(xs->state);
>> struct xsk_queue *q = NULL;
>>
>> - if (READ_ONCE(xs->state) != XSK_READY)
>> + if (state != XSK_READY && state != XSK_BOUND)
>> return -EBUSY;
>>
>> if (offset == XDP_PGOFF_RX_RING) {
>> @@ -1314,9 +1315,11 @@ static int xsk_mmap(struct file *file, struct socket *sock,
>> /* Matches the smp_wmb() in XDP_UMEM_REG */
>> smp_rmb();
>> if (offset == XDP_UMEM_PGOFF_FILL_RING)
>> - q = READ_ONCE(xs->fq_tmp);
>> + q = READ_ONCE(state == XSK_READY ? xs->fq_tmp :
>> + xs->pool->fq);
>> else if (offset == XDP_UMEM_PGOFF_COMPLETION_RING)
>> - q = READ_ONCE(xs->cq_tmp);
>> + q = READ_ONCE(state == XSK_READY ? xs->cq_tmp :
>> + xs->pool->cq);

This triggers a build error:

[...]
CC drivers/acpi/fan_attr.o
CC net/ipv6/syncookies.o
../net/xdp/xsk.c:1318:8: error: cannot take the address of an rvalue of type 'struct xsk_queue *'
q = READ_ONCE(state == XSK_READY ? xs->fq_tmp :
^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../include/asm-generic/rwonce.h:50:2: note: expanded from macro 'READ_ONCE'
__READ_ONCE(x); \
^ ~
../include/asm-generic/rwonce.h:44:70: note: expanded from macro '__READ_ONCE'
#define __READ_ONCE(x) (*(const volatile __unqual_scalar_typeof(x) *)&(x))
^ ~
../net/xdp/xsk.c:1321:8: error: cannot take the address of an rvalue of type 'struct xsk_queue *'
q = READ_ONCE(state == XSK_READY ? xs->cq_tmp :
^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../include/asm-generic/rwonce.h:50:2: note: expanded from macro 'READ_ONCE'
__READ_ONCE(x); \
^ ~
../include/asm-generic/rwonce.h:44:70: note: expanded from macro '__READ_ONCE'
#define __READ_ONCE(x) (*(const volatile __unqual_scalar_typeof(x) *)&(x))
^ ~
2 errors generated.
make[4]: *** [../scripts/Makefile.build:252: net/xdp/xsk.o] Error 1
make[4]: *** Waiting for unfinished jobs....
CC fs/fs_types.o
CC kernel/bpf/offload.o
AR net/mpls/built-in.a
CC net/mptcp/subflow.o
make[3]: *** [../scripts/Makefile.build:494: net/xdp] Error 2
make[3]: *** Waiting for unfinished jobs....

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