[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH RFC 4/4] xen/pvhvm: Make MSI IRQs work after kexec
On Wed, 16 Jul 2014, Konrad Rzeszutek Wilk wrote: > On Wed, Jul 16, 2014 at 11:01:55AM +0200, Vitaly Kuznetsov wrote: > > Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> 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! > > Thank you for quick turnaround with the answers! > > > > > 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-), > > I am wondering if that is related to in QEMU traditional: > > qemu-xen-trad: free all the pirqs for msi/msix when driver unloads > > (which in the upstream QEMU is 1d4fd4f0e2fc5dcae0c60e00cc9af95f52988050) > > If you have that patch in, is the PIRQ value correctly updated? > > > > > > 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 > > Good point. > > some cases when we see 'crap' instead of pirq here? > > For PCI passthrough devices they will be zero until they are enabled. > But I am not sure about the emulated devices, such as e1000 or such, which > would also go through this path (I think - do we have MSI devices that > we emulate in QEMU?) > > > > > 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. > > I concur. > > Stefano, do you recall why you used xen_irq_from_pirq instead of just > trusting the 'pirq' value? Was it to workaround broken QEMU? If I recall correctly the problem is that pirq == 0 is a valid pirq number. So the check pirq <= 0 is wrong. Can we rely on the fact that msg.data is always 0 on first read? If so, then we could simply: diff --git a/arch/x86/pci/xen.c b/arch/x86/pci/xen.c index 905956f..d824743 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 = xen_allocate_pirq_msi(dev, msidesc); if (pirq < 0) { irq = -ENODEV; _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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