Joby Poriyath
2013-Aug-15 13:05 UTC
[PATCH v4] interrupts: allow guest to set/clear MSI-X mask bit
Guest needs the ability to enable and disable MSI-X interrupts
by setting the MSI-X control bit, for a passed-through device.
Guest is allowed to write MSI-X mask bit only if Xen *thinks*
that mask is clear (interrupts enabled). If the mask is set by
Xen (interrupts disabled), writes to mask bit by the guest is
ignored.
Currently, a write to MSI-X mask bit by the guest is silently
ignored.
A likely scenario is where we have a 82599 SR-IOV nic passed
through to a guest. From the guest if you do
ifconfig <ETH_DEV> down
ifconfig <ETH_DEV> up
the interrupts remain masked. On VF reset, the mask bit is set
by the controller. At this point, Xen is not aware that mask is set.
However, interrupts are enabled by VF driver by clearing the mask
bit by writing directly to BAR3 region containing the MSI-X table.
From dom0, we can verify that
interrupts are being masked using ''xl debug-keys M''.
Initially, guest was allowed to modify MSI-X bit.
Later this behaviour was changed.
See changeset 74c213c506afcd74a8556dd092995fd4dc38b225.
Signed-off-by: Joby Poriyath <joby.poriyath@citrix.com>
---
xen/arch/x86/hvm/vmsi.c | 60 ++++++++++++++++++++++++++++++++++++-----------
1 file changed, 46 insertions(+), 14 deletions(-)
diff --git a/xen/arch/x86/hvm/vmsi.c b/xen/arch/x86/hvm/vmsi.c
index 36de312..67c504d 100644
--- a/xen/arch/x86/hvm/vmsi.c
+++ b/xen/arch/x86/hvm/vmsi.c
@@ -169,6 +169,7 @@ struct msixtbl_entry
uint32_t msi_ad[3]; /* Shadow of address low, high and data */
} gentries[MAX_MSIX_ACC_ENTRIES];
struct rcu_head rcu;
+ struct pirq *pirq;
};
static DEFINE_RCU_READ_LOCK(msixtbl_rcu_lock);
@@ -254,6 +255,8 @@ static int msixtbl_write(struct vcpu *v, unsigned long
address,
void *virt;
unsigned int nr_entry, index;
int r = X86EMUL_UNHANDLEABLE;
+ unsigned long flags, orig;
+ struct irq_desc *desc;
if ( len != 4 || (address & 3) )
return r;
@@ -283,22 +286,49 @@ static int msixtbl_write(struct vcpu *v, unsigned long
address,
if ( !virt )
goto out;
- /* Do not allow the mask bit to be changed. */
-#if 0 /* XXX
- * As the mask bit is the only defined bit in the word, and as the
- * host MSI-X code doesn''t preserve the other bits anyway, doing
- * this is pointless. So for now just discard the write (also
- * saving us from having to determine the matching irq_desc).
- */
- spin_lock_irqsave(&desc->lock, flags);
+ desc = pirq_spin_lock_irq_desc(entry->pirq, &flags);
+ if ( !desc )
+ goto out;
+
+ if ( !desc->msi_desc )
+ goto unlock;
+
orig = readl(virt);
- val &= ~PCI_MSIX_VECTOR_BITMASK;
- val |= orig & PCI_MSIX_VECTOR_BITMASK;
+
+ /*
+ * Do not allow guest to modify MSI-X control bit if it is masked
+ * by Xen. We''ll only handle the case where Xen thinks that
+ * bit is unmasked, but hardware has silently masked the bit
+ * (in case of SR-IOV VF reset, etc). On the other hand, if Xen
+ * thinks that the bit is masked, but it''s really not,
+ * we log a warning.
+ */
+ if ( desc->msi_desc->msi_attrib.masked )
+ {
+ if ( !(orig & PCI_MSIX_VECTOR_BITMASK) )
+ printk(XENLOG_WARNING "MSI-X control bit is unmasked
when"
+ " it is expected to be masked
[%04x:%02x:%02x.%01x]\n",
+ entry->pdev->seg, entry->pdev->bus,
+ PCI_SLOT(entry->pdev->devfn),
+ PCI_FUNC(entry->pdev->devfn));
+
+ goto unlock;
+ }
+
+ /*
+ * The mask bit is the only defined bit in the word. But we
+ * ought to preserve the reserved bits. Clearing the reserved
+ * bits can result in undefined behaviour (see PCI Local Bus
+ * Specification revision 2.3).
+ */
+ val &= PCI_MSIX_VECTOR_BITMASK;
+ val |= (orig & ~PCI_MSIX_VECTOR_BITMASK);
writel(val, virt);
- spin_unlock_irqrestore(&desc->lock, flags);
-#endif
+unlock:
+ spin_unlock_irqrestore(&desc->lock, flags);
r = X86EMUL_OKAY;
+
out:
rcu_read_unlock(&msixtbl_rcu_lock);
return r;
@@ -328,7 +358,8 @@ const struct hvm_mmio_handler msixtbl_mmio_handler = {
static void add_msixtbl_entry(struct domain *d,
struct pci_dev *pdev,
uint64_t gtable,
- struct msixtbl_entry *entry)
+ struct msixtbl_entry *entry,
+ struct pirq *pirq)
{
u32 len;
@@ -342,6 +373,7 @@ static void add_msixtbl_entry(struct domain *d,
entry->table_len = len;
entry->pdev = pdev;
entry->gtable = (unsigned long) gtable;
+ entry->pirq = pirq;
list_add_rcu(&entry->list, &d->arch.hvm_domain.msixtbl_list);
}
@@ -404,7 +436,7 @@ int msixtbl_pt_register(struct domain *d, struct pirq *pirq,
uint64_t gtable)
entry = new_entry;
new_entry = NULL;
- add_msixtbl_entry(d, pdev, gtable, entry);
+ add_msixtbl_entry(d, pdev, gtable, entry, pirq);
found:
atomic_inc(&entry->refcnt);
--
1.7.10.4
Jan Beulich
2013-Aug-15 13:25 UTC
Re: [PATCH v4] interrupts: allow guest to set/clear MSI-X mask bit
>>> On 15.08.13 at 15:05, Joby Poriyath <joby.poriyath@citrix.com> wrote: > --- a/xen/arch/x86/hvm/vmsi.c > +++ b/xen/arch/x86/hvm/vmsi.c > @@ -169,6 +169,7 @@ struct msixtbl_entry > uint32_t msi_ad[3]; /* Shadow of address low, high and data */ > } gentries[MAX_MSIX_ACC_ENTRIES]; > struct rcu_head rcu; > + struct pirq *pirq;Sill lacking the constification that Andrew suggested (and withdrew for apparently no reason). Jan
Joby Poriyath
2013-Aug-15 13:41 UTC
Re: [PATCH v4] interrupts: allow guest to set/clear MSI-X mask bit
On Thu, Aug 15, 2013 at 02:25:43PM +0100, Jan Beulich wrote:> >>> On 15.08.13 at 15:05, Joby Poriyath <joby.poriyath@citrix.com> wrote: > > --- a/xen/arch/x86/hvm/vmsi.c > > +++ b/xen/arch/x86/hvm/vmsi.c > > @@ -169,6 +169,7 @@ struct msixtbl_entry > > uint32_t msi_ad[3]; /* Shadow of address low, high and data */ > > } gentries[MAX_MSIX_ACC_ENTRIES]; > > struct rcu_head rcu; > > + struct pirq *pirq; > > Sill lacking the constification that Andrew suggested (and withdrew > for apparently no reason).Ah, I''m extremely sorry. I missed this. I''ll send the updated patch.> > Jan >Joby