Messages in this thread Patch in this message | | | From | Vitaly Kuznetsov <> | Subject | Re: [PATCH RFC 4/4] xen/pvhvm: Make MSI IRQs work after kexec | Date | Wed, 16 Jul 2014 11:01:55 +0200 |
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Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> writes:
> On Tue, Jul 15, 2014 at 03:40:40PM +0200, Vitaly Kuznetsov wrote: >> When kexec was peformed MSI IRQs for passthrough-ed devices were already >> mapped and we see non-zero pirq extracted from MSI msg. xen_irq_from_pirq() >> fails as we have no IRQ mapping information for that. Requesting for new >> mapping with __write_msi_msg() does not result in MSI IRQ being remapped so >> we don't recieve these IRQs. > > receive >
Thanks for your comments!
> How come '__write_msi_msg' does not result in new MSI IRQs? >
Actually that was the hidden question in my RFC :-)
Let me describe what I see. When normal boot is performed we have the following in xen_hvm_setup_msi_irqs():
__read_msi_msg() pirq -> 0
then we allocate new pirq with pirq = xen_allocate_pirq_msi() pirq -> 54
and we have the following mapping: xen: msi --> pirq=54 --> irq=72
in 'xl debug-keys i': (XEN) IRQ: 29 affinity:04 vec:b9 type=PCI-MSI status=00000030 in-flight=0 domain-list=7: 54(----),
After kexec we see the following: __read_msi_msg() pirq -> 54
but as xen_irq_from_pirq() fails we follow the same path allocating new pirq: pirq = xen_allocate_pirq_msi() pirq -> 55
and we have the following mapping: xen: msi --> pirq=55 --> irq=75
However (afaict) mapping in xen wasn't updated:
in 'xl debug-keys i': (XEN) IRQ: 29 affinity:02 vec:b9 type=PCI-MSI status=00000030 in-flight=0 domain-list=7: 54(--M-),
> Is it fair to state that your code ends up reading the MSI IRQ (PIRQ) > from the device and updating the internal PIRQ<->IRQ code to match > with the reality? >
Yea, 'always trust the device'.
>> >> RFC: I wasn't able to understand why commit af42b8d1 which introduced >> xen_irq_from_pirq() check in xen_hvm_setup_msi_irqs() is checking that instead >> of checking pirq > 0 as if the mapping was already done (and we have pirq>0 here) >> we don't need to request for a new pirq. We're loosing existing PIRQ and I'm also >> not sure when __write_msi_msg() with new PIRQ will result in new mapping. > > We don't request a new pirq. We end up returning before we call xen_allocate_pirq_msi. > At least that is how the commit you mentioned worked. >
I meant to say that in case we have pirq > 0 from __read_msi_msg() but xen_irq_from_pirq(pirq) fails (kexec-only case?) we always do xen_allocate_pirq_msi() which brings us new pirq.
> In regards to why using 'xen_irq_from_pirq' instead of just checking the PIRQ - is > that we might be called twice by a buggy driver. As such we want to check > our PIRQ<->IRQ to figure this out.
But if we're called twice we'll see the same pirq, right? Or there are some cases when we see 'crap' instead of pirq here?
I think it would be nice to use the same pirq after kexec instead of allocating a new one even in case we can make remapping work.
Thanks for your comments again!
>> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com> >> --- >> arch/x86/pci/xen.c | 3 +-- >> 1 file changed, 1 insertion(+), 2 deletions(-) >> >> diff --git a/arch/x86/pci/xen.c b/arch/x86/pci/xen.c >> index 905956f..685e8f1 100644 >> --- a/arch/x86/pci/xen.c >> +++ b/arch/x86/pci/xen.c >> @@ -231,8 +231,7 @@ static int xen_hvm_setup_msi_irqs(struct pci_dev *dev, int nvec, int type) >> __read_msi_msg(msidesc, &msg); >> pirq = MSI_ADDR_EXT_DEST_ID(msg.address_hi) | >> ((msg.address_lo >> MSI_ADDR_DEST_ID_SHIFT) & 0xff); >> - if (msg.data != XEN_PIRQ_MSI_DATA || >> - xen_irq_from_pirq(pirq) < 0) { >> + if (msg.data != XEN_PIRQ_MSI_DATA || pirq <= 0) { >> pirq = xen_allocate_pirq_msi(dev, msidesc); >> if (pirq < 0) { >> irq = -ENODEV; >> -- >> 1.9.3 >>
-- Vitaly
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