I'm currently adding mmap support to af_netlink based on the
af_packet implementation and I'm wondering about this code in
tpacket_rcv():
h->tp_status = status;
smp_mb();
{
struct page *p_start, *p_end;
u8 *h_end = (u8 *)h + macoff + snaplen - 1;
p_start = virt_to_page(h);
p_end = virt_to_page(h_end);
while (p_start <= p_end) {
flush_dcache_page(p_start);
p_start++;
}
}
Shouldn't the flushing be done in reverse order to make sure
that the page containing tp_status is flushed last and userspace
doesn't start looking at following pages before all dcache entries
are flushed?
A related question: Documentation/cachetlb.txt mentions that
flushing also needs to be done for reading of shared+writable
mapped pages, so it seems like we also need to call flush_dcache_page
before the tp_status check earlier in that function and packet_poll().
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