linux-kernel - Re: [PATCH v2 2/2] Intel-IOMMU, intr-remap: source-id checking

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Date:	Wed, 20 May 2009 10:21:14 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Joerg Roedel <joerg.roedel@....com>
Cc:	Weidong Han <weidong.han@...el.com>, dwmw2@...radead.org,
	suresh.b.siddha@...el.com, linux-kernel@...r.kernel.org,
	iommu@...ts.linux-foundation.org, kvm@...r.kernel.org
Subject: Re: [PATCH v2 2/2] Intel-IOMMU, intr-remap: source-id checking


* Eric W. Biederman <ebiederm@...ssion.com> wrote:

> Ingo Molnar <mingo@...e.hu> writes:
> 
> > * Weidong Han <weidong.han@...el.com> wrote:
> >
> >> To support domain-isolation usages, the platform hardware must be 
> >> capable of uniquely identifying the requestor (source-id) for each 
> >> interrupt message. Without source-id checking for interrupt 
> >> remapping , a rouge guest/VM with assigned devices can launch 
> >> interrupt attacks to bring down anothe guest/VM or the VMM itself.
> >> 
> >> This patch adds source-id checking for interrupt remapping, and 
> >> then really isolates interrupts for guests/VMs with assigned 
> >> devices.
> >> 
> >> Because PCI subsystem is not initialized yet when set up IOAPIC 
> >> entries, use read_pci_config_byte to access PCI config space 
> >> directly.
> >> 
> >> Signed-off-by: Weidong Han <weidong.han@...el.com>
> >> ---
> >>  arch/x86/kernel/apic/io_apic.c |    6 +++
> >>  drivers/pci/intr_remapping.c   |   90 ++++++++++++++++++++++++++++++++++++++-
> >>  drivers/pci/intr_remapping.h   |    2 +
> >>  include/linux/dmar.h           |   11 +++++
> >>  4 files changed, 106 insertions(+), 3 deletions(-)
> >
> > Code structure looks nice now. (and i susect you have tested this on 
> > real and relevant hardware?) I've Cc:-ed Eric too ... does this 
> > direction look good to you too Eric?
> 
> Being a major nitpick, I have to point out that the code is not 
> structured to support other iommus, and I think AMD has one that 
> can do this as well.

(Joerg Cc:-ed)

> The early pci reading of the bus is just wrong.  What happens if 
> the pci layer decided to renumber things?  It looks like we have a 
> real dependency on pci there and are avoiding sorting it out with 
> this.

Yes ... but is there much we can do about this bootstrap dependency? 
We want to enable the IO-APIC very early in its final form. There's 
quite a bit of IRQ functionality that doesnt go via the PCI layer, 
and which is being relied on by early bootup. The timer irq must 
work, etc.

> Hmm.  But that is what we use in setup_ioapic_sid.... I expect the 
> right solution is to delay enabling ioapic entries until driver 
> enable them.  That could also reduce screaming irqs during bootup 
> in the kdump case.

Yes, and note that we are moving in that direction in tip:irq/numa 
(Yinghai Cc:-ed) - we are delaying IRQ setup to the very last 
moment. We recently got rid of 32-bit IRQ compression in that branch 
as well and the IRQ vectoring code is now unified between 64-bit and 
32-bit so it's nify and you might want to check it and look for 
holes ...

( The motivation there was different: delay allocation of the 
  irq_desc so that we can make it NUMA-local - but it has the same 
  general effect. )

> set_msi_sid looks wrong.  The comment are unhelpful. irte->svt 
> should get an enum value or a deine (removing the repeated 
> explanations of the magic value) and then we could have room to 
> explain why we are doing what we are doing.

(yes, it probably wants a helper method - i pointed these smaller 
details out in my review.)

> Not finding an upstream pcie_bridge and then concluding we are a 
> pcie device seems bogus.
> 
> Why if we do have an upstream pcie bridge do we only want to do a 
> bus range verification instead of checking just for the bus 
> :devfn?
> 
> The legacy PCI case seems even stranger.

Good points. Would be nice to get an ack from the PCI folks to make 
sure these bits are sane.

> ....
> 
> The table of apic information by apic_id also seems wrong.  Don't 
> we have chip_data or something that should point it that we can 
> get from the irq?

->chip_data is already used for io-apic configuration bits - if it's 
reused then the right way to do it is to extend struct irq_cfg in 
arch/x86/kernel/apic/io_apic.c.

	Ingo
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