PCI memory sync question (kvm,dpdk,e1000,packet stalled)

[ASM <asm@asm.pp.ru>]

Hi folks!

I trying solve the problem, with packets stopping (e1000,tap,kvm).
My studies led to the following:
1. From flatview_write_continue() I see, what e1000 writes the number
"7" to the STAT register.
2. The driver from target OS reads STAT register with number "7" and
writes to the register the number "0".
3. From flatview_write_continue() (I make edits):
            memcpy(ptr, buf, l);
            new1=ptr[0xc];
            usleep(100);
            new2=ptr[0xc];
            invalidate_and_set_dirty(mr, addr1, l);
            new3=ptr[0xc];
printf("Old: %i, new1, %i, new2: %i, new3: %i\n", old,new1,new2,new3);

I see what memory in first printf is "7", but after usleep() is "0".
Do I understand correctly that this should not be? Or RCU lock
suggests the ability to the multiple writers?

The problem is that qemu(e1000) writes the number 7, after which
target(dpdk driver) reads 7, on the basis of this it writes the number
0, but as a result (extremely rarely), the value STATUS still remains
7. Therefore, packet processing is interrupted. This behavior is
observed only on kvm (it is not observed on tcg).

Please help with advice or ideas.

P.S. I started a bug report earlier. There is more detailed
information. In my broken English:
bugs.launchpad.net/qemu/+bug/1853123

---
Best regards,
Leonid Myravjev