Re: [Xen-devel] [RFC] e1000: Don't save writes to ICS/ICR masked by IMS

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Thu, Sep 01, 2016 at 10:57:48AM -0700, Ed Swierk wrote:
> Windows 8, 10 and Server 2012 guests hang intermittently while booting
> on Xen 4.5.3 with 1 vCPU and 4 e1000 vNICs, shortly after the Windows
> logo appears and the little dots start spinning.
> 
> Running strace on qemu shows its main thread doing the following every
> couple of milliseconds:
> 
>  ppoll([..., {fd=30</dev/xen/evtchn>, events=POLLIN|POLLERR|POLLHUP},
>         ...], ...) = 1 ([{fd=30, revents=POLLIN}], ...)
>  read(30</dev/xen/evtchn>, "^\0\0\0", 4) = 4
>  write(30</dev/xen/evtchn>, "^\0\0\0", 4) = 4
>  ioctl(30</dev/xen/evtchn>, IOCTL_EVTCHN_NOTIFY, 0x7f1f9449d310) = 0
>  clock_gettime(CLOCK_MONOTONIC, {6937, 449468262}) = 0
>  clock_gettime(CLOCK_MONOTONIC, {6937, 449582903}) = 0
>  gettimeofday({1472251376, 673434}, NULL) = 0
>  clock_gettime(CLOCK_MONOTONIC, {6937, 449856205}) = 0
>  gettimeofday({1472251376, 673679}, NULL) = 0
> 
> The event channel (identified by '^' or 94 in this example) is always
> the third of the domain's four channels.
> 
> Two recent qemu patches (http://git.qemu.org/?p=qemu.git;h=9596ef7c and
> http://git.qemu.org/?p=qemu.git;h=74004e8c) seem to address similar
> issues, but don't help in this case.
> 
> The proposed fix from
> https://bugzilla.redhat.com/show_bug.cgi?id=874406#c78 makes the hang
> go away. It's not clear to me why it works, or if it's just papering
> over a bug elsewhere, or if there are any possible side effects.

CC-ing Denis.


Is the fix below based on reading the spec or more of instrumenting?

Thanks.
> 
> Suggested-by: Andrew Jones <drjones@xxxxxxxxxx>
> Signed-off-by: Ed Swierk <eswierk@xxxxxxxxxxxxxxxxxx>
> 
> diff --git a/hw/net/e1000.c b/hw/net/e1000.c
> index 6eac66d..c891b67 100644
> --- a/hw/net/e1000.c
> +++ b/hw/net/e1000.c
> @@ -293,6 +293,8 @@ set_interrupt_cause(E1000State *s, int index, uint32_t 
> val)
>      uint32_t pending_ints;
>      uint32_t mit_delay;
>  
> +    val &= s->mac_reg[IMS];
> +
>      s->mac_reg[ICR] = val;
>  
>      /*
> @@ -305,7 +307,7 @@ set_interrupt_cause(E1000State *s, int index, uint32_t 
> val)
>       */
>      s->mac_reg[ICS] = val;
>  
> -    pending_ints = (s->mac_reg[IMS] & s->mac_reg[ICR]);
> +    pending_ints = s->mac_reg[ICR];
>      if (!s->mit_irq_level && pending_ints) {
>          /*
>           * Here we detect a potential raising edge. We postpone raising the
> 
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