From: Thomas Gleixner <tglx@linutronix.de>
To: Salvatore Bonaccorso <carnil@debian.org>,
Jeremi Piotrowski <jpiotrowski@linux.microsoft.com>
Cc: Dusty Mabe <dustymabe@redhat.com>, Stefan Roese <sr@denx.de>,
linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
Bjorn Helgaas <bhelgaas@google.com>,
Michal Simek <michal.simek@xilinx.com>,
Marek Vasut <marex@denx.de>,
x86@kernel.org, maz@kernel.org,
Andrew Cooper <andrew.cooper3@citrix.com>,
Juergen Gross <jgross@suse.com>
Subject: Re: [tip: irq/urgent] PCI/MSI: Mask MSI-X vectors only on success
Date: Thu, 28 Apr 2022 15:48:03 +0200 [thread overview]
Message-ID: <87wnf9uxnw.ffs@tglx> (raw)
In-Reply-To: <87v8uuwhs4.ffs@tglx>
On Wed, Apr 27 2022 at 19:35, Thomas Gleixner wrote:
> On Wed, Apr 27 2022 at 09:59, Salvatore Bonaccorso wrote:
> XEN guests do not use the common PCI mask/unmask machinery which would
> unmask the interrupt on request_irq().
>
> So I assume that the following happens:
>
> Guest Hypervisor
>
> msix_capabilities_init()
> ....
> alloc_irq()
> xen_magic() -> alloc_msix_interrupt()
> request_irq()
>
> msix_mask_all() -> trap
> do_magic()
> request_irq()
> unmask()
> xen_magic()
> unmask_evtchn() -> do_more_magic()
>
> So I assume further that msix_mask_all() actually is able to mask the
> interrupts in the hardware (ctrl word of the vector table) despite the
> hypervisor having allocated and requested the interrupt already.
>
> Nothing in XEN_HVM handles PCI/MSI[-X] mask/unmask in the guest, so I
> really have to ask why XEN_HVM does not disable PCI/MSI[-X] masking like
> XEN_PV does. I can only assume the answer is voodoo...
>
> Maybe the XEN people have some more enlightened answers to that.
So I was talking to Juergen about this and he agrees, that for the case
where a XEN HVM guest uses the PIRQ/Eventchannel mechanism PCI/MSI[-X]
masking should be disabled like it is done for XEN PV.
Why the hypervisor grants the mask write is still mysterious, but I
leave that to the folks who can master the XEN voodoo.
I'll send out a patch in minute.
Thanks,
tglx
next prev parent reply other threads:[~2022-04-28 13:48 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20211210161025.3287927-1-sr@denx.de>
2021-12-14 12:28 ` [tip: irq/urgent] PCI/MSI: Mask MSI-X vectors only on success tip-bot2 for Stefan Roese
2022-03-14 16:36 ` Jeremi Piotrowski
2022-03-14 16:49 ` Stefan Roese
2022-03-14 17:04 ` Dusty Mabe
2022-03-14 20:29 ` Jeremi Piotrowski
2022-04-27 7:59 ` Salvatore Bonaccorso
2022-04-27 17:35 ` Thomas Gleixner
2022-04-28 13:48 ` Thomas Gleixner [this message]
2022-04-28 13:50 ` [PATCH] x86/pci/xen: Disable PCI/MSI[-X] masking for XEN_HVM guests Thomas Gleixner
2022-05-01 8:12 ` [tip: x86/urgent] " tip-bot2 for Thomas Gleixner
2022-04-28 18:43 ` [tip: irq/urgent] PCI/MSI: Mask MSI-X vectors only on success Salvatore Bonaccorso
2022-04-29 6:37 ` Salvatore Bonaccorso
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