On Wed, Dec 19, 2018 at 09:57:51AM +0100, Roger Pau Monné wrote:
>On Tue, Dec 18, 2018 at 10:43:37PM +0800, Chao Gao wrote:
>> I find some pass-thru devices don't work any more across guest
>> reboot. Assigning it to another domain also meets the same issue. And
>> the only way to make it work again is un-binding and binding it to
>> pciback. Someone reported this issue one year ago [1].
>>
>> If the device's driver doesn't disable MSI-X during shutdown or qemu is
>> killed/crashed before the domain shutdown, this domain's pirq won't be
>> unmapped. Then xen takes over this work, unmapping all pirq-s, when
>> destroying guest. But as pciback has already disabled meory decoding before
>> xen unmapping pirq, Xen has to sets the host_maskall flag and maskall bit
>> to mask a MSI rather than sets maskbit in MSI-x table. The call trace of
>> this process is:
>>
>> ->arch_domain_destroy
>> ->free_domain_pirqs
>> ->unmap_domain_pirq (if pirq isn't unmapped by qemu)
>> ->pirq_guest_force_unbind
>> ->__pirq_guest_unbind
>> ->mask_msi_irq(=desc->handler->disable())
>> ->the warning in msi_set_mask_bit()
>>
>> The host_maskall bit will prevent guests from clearing the maskall bit
>> even the device is assigned to another guest later. Then guests cannot
>> receive MSIs from this device.
>>
>> To fix this issue, a pirq is unmapped before memory decoding is disabled by
>> pciback. Specifically, when a device is detached from a guest, all
>> established
>> mappings between pirq and msi are destroying before changing the ownership.
>>
>> [1]:
>> https://lists.xenproject.org/archives/html/xen-devel/2017-09/msg02520.html
>>
>> Signed-off-by: Chao Gao <[email protected]>
>> ---
>> Applied this patch, qemu would report the error below:
>> [00:05.0] msi_msix_disable: Error: Unbinding of MSI-X failed. (err: 1,
>> pirq: 302, gvec: 0xd5)
>> [00:05.0] msi_msix_disable: Error: Unbinding of MSI-X failed. (err: 1,
>> pirq: 301, gvec: 0xe5)
>> [00:04.0] msi_msix_disable: Error: Unbinding of MSI-X failed. (err: 1,
>> pirq: 359, gvec: 0x41)
>> [00:04.0] msi_msix_disable: Error: Unbinding of MSI-X failed. (err: 1,
>> pirq: 358, gvec: 0x51)
>>
>> Despite of the error, guest shutdown or device hotplug finishs smoothly.
>> It seems to me that qemu tries to unbind a msi which is already unbound by
>> the code added by this patch. I am not sure whether it is acceptable to
>> leave this error there.
>
>So QEMU would try to unmap IRQs after unbinding the device? I think
It seems to me yes. I don't know the reason right now. maybe because it
is an asynchronous process?
>QEMU should be fixed to first unmap the IRQs and then unbind the
>device.
Yes. Agree.
>
>As long as this doesn't affect QEMU functionality I guess the Xen side
>can be committed, but ideally a QEMU patch to avoid those error
>messages should be committed at the same time.
>
>> ---
>> xen/drivers/passthrough/io.c | 57
>> +++++++++++++++++++++++++++++--------------
>> xen/drivers/passthrough/pci.c | 49 +++++++++++++++++++++++++++++++++++++
>> xen/include/xen/iommu.h | 1 +
>> 3 files changed, 89 insertions(+), 18 deletions(-)
>>
>> diff --git a/xen/drivers/passthrough/io.c b/xen/drivers/passthrough/io.c
>> index a6eb8a4..56ee1ef 100644
>> --- a/xen/drivers/passthrough/io.c
>> +++ b/xen/drivers/passthrough/io.c
>> @@ -619,6 +619,42 @@ int pt_irq_create_bind(
>> return 0;
>> }
>>
>> +static void pt_irq_destroy_bind_common(struct domain *d, struct pirq *pirq)
>> +{
>> + struct hvm_pirq_dpci *pirq_dpci = pirq_dpci(pirq);
>> +
>> + ASSERT(spin_is_locked(&d->event_lock));
>> +
>> + if ( pirq_dpci && (pirq_dpci->flags & HVM_IRQ_DPCI_MAPPED) &&
>> + list_empty(&pirq_dpci->digl_list) )
>> + {
>> + pirq_guest_unbind(d, pirq);
>> + msixtbl_pt_unregister(d, pirq);
>> + if ( pt_irq_need_timer(pirq_dpci->flags) )
>> + kill_timer(&pirq_dpci->timer);
>> + pirq_dpci->flags = 0;
>> + /*
>> + * See comment in pt_irq_create_bind's PT_IRQ_TYPE_MSI before the
>> + * call to pt_pirq_softirq_reset.
>> + */
>> + pt_pirq_softirq_reset(pirq_dpci);
>> +
>> + pirq_cleanup_check(pirq, d);
>> + }
>> +}
>> +
>> +void pt_irq_destroy_bind_msi(struct domain *d, struct pirq *pirq)
>> +{
>> + struct hvm_pirq_dpci *pirq_dpci = pirq_dpci(pirq);
>> +
>> + ASSERT(spin_is_locked(&d->event_lock));
>> +
>> + if ( pirq_dpci && pirq_dpci->gmsi.posted )
>> + pi_update_irte(NULL, pirq, 0);
>> +
>> + pt_irq_destroy_bind_common(d, pirq);
>> +}
>> +
>> int pt_irq_destroy_bind(
>> struct domain *d, const struct xen_domctl_bind_pt_irq *pt_irq_bind)
>> {
>> @@ -727,26 +763,11 @@ int pt_irq_destroy_bind(
>> }
>> else
>> what = "bogus";
>> - }
>> - else if ( pirq_dpci && pirq_dpci->gmsi.posted )
>> - pi_update_irte(NULL, pirq, 0);
>> -
>> - if ( pirq_dpci && (pirq_dpci->flags & HVM_IRQ_DPCI_MAPPED) &&
>> - list_empty(&pirq_dpci->digl_list) )
>> - {
>> - pirq_guest_unbind(d, pirq);
>> - msixtbl_pt_unregister(d, pirq);
>> - if ( pt_irq_need_timer(pirq_dpci->flags) )
>> - kill_timer(&pirq_dpci->timer);
>> - pirq_dpci->flags = 0;
>> - /*
>> - * See comment in pt_irq_create_bind's PT_IRQ_TYPE_MSI before the
>> - * call to pt_pirq_softirq_reset.
>> - */
>> - pt_pirq_softirq_reset(pirq_dpci);
>>
>> - pirq_cleanup_check(pirq, d);
>> + pt_irq_destroy_bind_common(d, pirq);
>> }
>> + else
>> + pt_irq_destroy_bind_msi(d, pirq);
>>
>> spin_unlock(&d->event_lock);
>>
>> diff --git a/xen/drivers/passthrough/pci.c b/xen/drivers/passthrough/pci.c
>> index 1277ce2..88a8007 100644
>> --- a/xen/drivers/passthrough/pci.c
>> +++ b/xen/drivers/passthrough/pci.c
>> @@ -368,6 +368,7 @@ static struct pci_dev *alloc_pdev(struct pci_seg *pseg,
>> u8 bus, u8 devfn)
>> return NULL;
>> }
>> spin_lock_init(&msix->table_lock);
>> + msix->warned = DOMID_INVALID;
>> pdev->msix = msix;
>> }
>>
>> @@ -1514,6 +1515,52 @@ static int assign_device(struct domain *d, u16 seg,
>> u8 bus, u8 devfn, u32 flag)
>> return rc;
>> }
>>
>> +/*
>> + * Unmap established mappings between domain's pirq and device's MSI.
>> + * These mappings were set up by qemu/guest and are expected to be
>> + * destroyed when changing the device's ownership.
>> + */
>> +static void pci_unmap_msi(struct pci_dev *pdev)
>> +{
>> + struct msi_desc *entry, *tmp;
>> +
>> + ASSERT(pcidevs_locked());
>> +
>> + if ( !pdev->domain )
>> + return;
>> +
>> + spin_lock(&pdev->domain->event_lock);
>> + list_for_each_entry_safe( entry, tmp, &pdev->msi_list, list )
>
>Do you really need the _safe version here? Couldn't you even use:
Don't need the _safe version.
>
>while ( (entry = list_first_entry_or_null(...)) != NULL )
>...
I think it is the same with list_for_each_entry(). Any reason makes you think
this one would be better?
>
>> + {
>> + struct pirq *info;
>> + struct hvm_pirq_dpci *pirq_dpci;
>> + int pirq = domain_irq_to_pirq(pdev->domain, entry->irq), pirq_orig;
>> +
>> + pirq_orig = pirq;
>> +
>> + if ( !pirq )
>> + continue;
>> +
>> + /* For forcibly unmapped pirq, lookup radix tree with absolute
>> value */
>> + if ( pirq < 0)
>> + pirq = -pirq;
>
>I'm not sure I follow, the pirq hasn't been unmapped at this point
>yet?
Qemu (i.e. compromised qemu) has the ability to do this. Right? we can't
assert the pirq hasn't been unmapped here.
>
>> +
>> + info = pirq_info(pdev->domain, pirq);
>> + if ( !info )
>> + continue;
>> + pirq_dpci = pirq_dpci(info);
>> +
>> + if ( pirq_dpci &&
>> + (pirq_dpci->flags & HVM_IRQ_DPCI_MACH_MSI) &&
>> + (pirq_dpci->flags & HVM_IRQ_DPCI_GUEST_MSI) )
>> + pt_irq_destroy_bind_msi(pdev->domain, info);
>
>I think this is missing unbinding for group MSI interrupts, you should
>check the type and if it's MSI (not MSIX) iterate over the number of
>vectors in msi.nvec in order to unbind them?
Good catch.
Thanks
Chao
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