[Bug 238095] Current console input freezes in hyperv gen 2 VM after randon amount of time

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=238095

--- Comment #13 from Hans Petter Selasky <hselasky at FreeBSD.org> ---
Last time I was debugging something in this area, I found that the UART
registers, which appear emulated, have some races. For example if I was reading
the UART registers right before posting a doorbell on the mlx4en driver, the
hypervisor would reboot the image :-(

+       if (mlx4_crash != 0) {
+               while (1) {
+                       inb(0x3f8+5);
+               }
+       }
+       __raw_writel((__force u32)val,
+            &priv->mfunc.comm->slave_write);

I was not able to get to the bottom of this due to lack of interest from the
hypervisor developers.

This race happens only with N number of CPUs.

You may play around with inb() in the network driver code and see if you can
provoke a similar action.

--HPS

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