Re: xen vtd : set msi guest_masked 0 by default

From: David Woodhouse <dwmw2@infradead.org>
To: "Jianzhong,Chang" <changjzh@gmail.com>,
	keir@xen.org, jbeulich@suse.com, andrew.cooper3@citrix.com,
	xen-devel@lists.xen.org
Cc: Andra-Irina Paraschiv <andraprs@amazon.com>
Subject: Re: xen vtd : set msi guest_masked 0 by default
Date: Mon, 21 May 2018 12:46:19 +0100	[thread overview]
Message-ID: <1526903179.8186.43.camel@infradead.org> (raw)
In-Reply-To: <1453772092-24866-1-git-send-email-changjzh@gmail.com>

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On Tue, 2016-01-26 at 09:34 +0800, Jianzhong,Chang wrote:
> There are some problems when msi guest_masked is set to 1 by default.
> When guest os is windows 2008 r2 server,
> the device(eg X540-AT2 vf) is not initialized correctly.
> Host will always receive message like this :"VF Reset msg received from vf".
> Guest has network connectivity issues,
> and can not correctly receive/send the packet.

In other words "the guest doesn't get any interrupts from the NIC".

> So, guest_masked is set to 0 by default.

This seems consistent with the PCI spec, which says that "After reset,
the state of all implemented Mask and Pending bits is 0 (no vectors are
masked and no messages are pending)."

That's what we *used* to have in Xen, before these commits changed it
to assume that IRQs were guest-masked by default:

https://xenbits.xen.org/gitweb/?p=xen.git;a=commitdiff;h=ad28e42bd1d28d746988ed71654e8aa670629753
https://xenbits.xen.org/gitweb/?p=xen.git;a=commitdiff;h=84d6add5593d865736831d150da7c38588f669f6

> --- a/xen/arch/x86/msi.c
> +++ b/xen/arch/x86/msi.c
> @@ -512,7 +512,7 @@ void guest_mask_msi_irq(struct irq_desc *desc, bool_t mask)
>  
>  static unsigned int startup_msi_irq(struct irq_desc *desc)
>  {
> -    if ( unlikely(!msi_set_mask_bit(desc, 0, !!(desc->status & IRQ_GUEST))) )
> +    if ( unlikely(!msi_set_mask_bit(desc, 0, 0) ))
>          WARN();
>      return 0;
>  }

In testing, this part actually seems to make the difference in
practice. Interrupts now work, and Windows guests have connectivity
again.

> @@ -972,7 +972,7 @@ static int msix_capability_init(struct pci_dev *dev,
>          entry->msi_attrib.entry_nr = msi->entry_nr;
>          entry->msi_attrib.maskbit = 1;
>          entry->msi_attrib.host_masked = 1;
> -        entry->msi_attrib.guest_masked = 1;
> +        entry->msi_attrib.guest_masked = 0;
>          entry->msi_attrib.pos = pos;
>          entry->irq = msi->irq;
>          entry->dev = dev;

That also seems correct though, since it reflects the actual state we
intend to emulate.

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