[Xen-devel] [PATCH for-4.13] x86/passthrough: fix migration of MSI when using posted interrupts

Roger Pau Monne posted 1 patch 1 week ago
Patches applied successfully (tree, apply log)
git fetch https://github.com/patchew-project/xen tags/patchew/20191009090539.2141-1-roger.pau@citrix.com
xen/arch/x86/hvm/vlapic.c              |  6 +++---
xen/drivers/passthrough/io.c           | 10 +++++++---
xen/drivers/passthrough/vtd/intremap.c | 15 ++++++++-------
xen/include/asm-x86/hvm/vlapic.h       |  2 ++
xen/include/asm-x86/iommu.h            |  2 +-
5 files changed, 21 insertions(+), 14 deletions(-)

[Xen-devel] [PATCH for-4.13] x86/passthrough: fix migration of MSI when using posted interrupts

Posted by Roger Pau Monne 1 week ago
When using posted interrupts and the guest migrates MSI from vCPUs Xen
needs to flush any pending PIRR vectors on the previous vCPU, or else
those vectors could get wrongly injected at a later point when the MSI
fields are already updated.

Rename sync_pir_to_irr to vlapic_sync_pir_to_irr and export it so it
can be called when updating the posted interrupt descriptor field in
pi_update_irte. While there also remove the unlock_out from
pi_update_irte, it's used in a single goto and removing it makes the
function smaller.

Note that PIRR is synced to IRR both in pt_irq_destroy_bind and
pt_irq_create_bind when the interrupt delivery data is being updated.

While there guard pi_update_irte with CONFIG_HVM since it's only used
with HVM guests.

Reported-by: Joe Jin <joe.jin@oracle.com>
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
Cc: Joe Jin <joe.jin@oracle.com>
Cc: Juergen Gross <jgross@suse.com>
---
I would like to see a bug fix for this issue in 4.13. The fix here only
affects posted interrupts, hence I think the risk of breaking anything
else is low.
---
 xen/arch/x86/hvm/vlapic.c              |  6 +++---
 xen/drivers/passthrough/io.c           | 10 +++++++---
 xen/drivers/passthrough/vtd/intremap.c | 15 ++++++++-------
 xen/include/asm-x86/hvm/vlapic.h       |  2 ++
 xen/include/asm-x86/iommu.h            |  2 +-
 5 files changed, 21 insertions(+), 14 deletions(-)

diff --git a/xen/arch/x86/hvm/vlapic.c b/xen/arch/x86/hvm/vlapic.c
index 9466258d6f..d255ad8db7 100644
--- a/xen/arch/x86/hvm/vlapic.c
+++ b/xen/arch/x86/hvm/vlapic.c
@@ -106,7 +106,7 @@ static void vlapic_clear_irr(int vector, struct vlapic *vlapic)
     vlapic_clear_vector(vector, &vlapic->regs->data[APIC_IRR]);
 }
 
-static void sync_pir_to_irr(struct vcpu *v)
+void vlapic_sync_pir_to_irr(struct vcpu *v)
 {
     if ( hvm_funcs.sync_pir_to_irr )
         alternative_vcall(hvm_funcs.sync_pir_to_irr, v);
@@ -114,7 +114,7 @@ static void sync_pir_to_irr(struct vcpu *v)
 
 static int vlapic_find_highest_irr(struct vlapic *vlapic)
 {
-    sync_pir_to_irr(vlapic_vcpu(vlapic));
+    vlapic_sync_pir_to_irr(vlapic_vcpu(vlapic));
 
     return vlapic_find_highest_vector(&vlapic->regs->data[APIC_IRR]);
 }
@@ -1493,7 +1493,7 @@ static int lapic_save_regs(struct vcpu *v, hvm_domain_context_t *h)
     if ( !has_vlapic(v->domain) )
         return 0;
 
-    sync_pir_to_irr(v);
+    vlapic_sync_pir_to_irr(v);
 
     return hvm_save_entry(LAPIC_REGS, v->vcpu_id, h, vcpu_vlapic(v)->regs);
 }
diff --git a/xen/drivers/passthrough/io.c b/xen/drivers/passthrough/io.c
index b292e79382..88188d2d7f 100644
--- a/xen/drivers/passthrough/io.c
+++ b/xen/drivers/passthrough/io.c
@@ -341,7 +341,7 @@ int pt_irq_create_bind(
     {
         uint8_t dest, delivery_mode;
         bool dest_mode;
-        int dest_vcpu_id;
+        int dest_vcpu_id, prev_vcpu_id = -1;
         const struct vcpu *vcpu;
         uint32_t gflags = pt_irq_bind->u.msi.gflags &
                           ~XEN_DOMCTL_VMSI_X86_UNMASKED;
@@ -411,6 +411,7 @@ int pt_irq_create_bind(
 
                 pirq_dpci->gmsi.gvec = pt_irq_bind->u.msi.gvec;
                 pirq_dpci->gmsi.gflags = gflags;
+                prev_vcpu_id = pirq_dpci->gmsi.dest_vcpu_id;
             }
         }
         /* Calculate dest_vcpu_id for MSI-type pirq migration. */
@@ -440,7 +441,8 @@ int pt_irq_create_bind(
         /* Use interrupt posting if it is supported. */
         if ( iommu_intpost )
             pi_update_irte(vcpu ? &vcpu->arch.hvm.vmx.pi_desc : NULL,
-                           info, pirq_dpci->gmsi.gvec);
+                           info, pirq_dpci->gmsi.gvec,
+                           prev_vcpu_id >= 0 ? d->vcpu[prev_vcpu_id] : NULL);
 
         if ( pt_irq_bind->u.msi.gflags & XEN_DOMCTL_VMSI_X86_UNMASKED )
         {
@@ -729,7 +731,9 @@ int pt_irq_destroy_bind(
             what = "bogus";
     }
     else if ( pirq_dpci && pirq_dpci->gmsi.posted )
-        pi_update_irte(NULL, pirq, 0);
+        pi_update_irte(NULL, pirq, 0,
+                       pirq_dpci->gmsi.dest_vcpu_id >= 0
+                       ? d->vcpu[pirq_dpci->gmsi.dest_vcpu_id] : NULL);
 
     if ( pirq_dpci && (pirq_dpci->flags & HVM_IRQ_DPCI_MAPPED) &&
          list_empty(&pirq_dpci->digl_list) )
diff --git a/xen/drivers/passthrough/vtd/intremap.c b/xen/drivers/passthrough/vtd/intremap.c
index bf846195c4..0f364e81b0 100644
--- a/xen/drivers/passthrough/vtd/intremap.c
+++ b/xen/drivers/passthrough/vtd/intremap.c
@@ -946,12 +946,13 @@ void intel_iommu_disable_eim(void)
         disable_qinval(drhd->iommu);
 }
 
+#if CONFIG_HVM
 /*
  * This function is used to update the IRTE for posted-interrupt
  * when guest changes MSI/MSI-X information.
  */
 int pi_update_irte(const struct pi_desc *pi_desc, const struct pirq *pirq,
-    const uint8_t gvec)
+    const uint8_t gvec, struct vcpu *prev)
 {
     struct irq_desc *desc;
     struct msi_desc *msi_desc;
@@ -964,8 +965,8 @@ int pi_update_irte(const struct pi_desc *pi_desc, const struct pirq *pirq,
     msi_desc = desc->msi_desc;
     if ( !msi_desc )
     {
-        rc = -ENODEV;
-        goto unlock_out;
+        spin_unlock_irq(&desc->lock);
+        return -ENODEV;
     }
     msi_desc->pi_desc = pi_desc;
     msi_desc->gvec = gvec;
@@ -974,10 +975,10 @@ int pi_update_irte(const struct pi_desc *pi_desc, const struct pirq *pirq,
 
     ASSERT(pcidevs_locked());
 
-    return msi_msg_write_remap_rte(msi_desc, &msi_desc->msg);
-
- unlock_out:
-    spin_unlock_irq(&desc->lock);
+    rc = msi_msg_write_remap_rte(msi_desc, &msi_desc->msg);
+    if ( !rc && prev )
+         vlapic_sync_pir_to_irr(prev);
 
     return rc;
 }
+#endif
diff --git a/xen/include/asm-x86/hvm/vlapic.h b/xen/include/asm-x86/hvm/vlapic.h
index dde66b4f0f..b0017d1dae 100644
--- a/xen/include/asm-x86/hvm/vlapic.h
+++ b/xen/include/asm-x86/hvm/vlapic.h
@@ -150,4 +150,6 @@ bool_t vlapic_match_dest(
     const struct vlapic *target, const struct vlapic *source,
     int short_hand, uint32_t dest, bool_t dest_mode);
 
+void vlapic_sync_pir_to_irr(struct vcpu *v);
+
 #endif /* __ASM_X86_HVM_VLAPIC_H__ */
diff --git a/xen/include/asm-x86/iommu.h b/xen/include/asm-x86/iommu.h
index 85741f7c96..314dcfbe47 100644
--- a/xen/include/asm-x86/iommu.h
+++ b/xen/include/asm-x86/iommu.h
@@ -119,7 +119,7 @@ static inline void iommu_disable_x2apic(void)
 extern bool untrusted_msi;
 
 int pi_update_irte(const struct pi_desc *pi_desc, const struct pirq *pirq,
-                   const uint8_t gvec);
+                   const uint8_t gvec, struct vcpu *prev);
 
 #endif /* !__ARCH_X86_IOMMU_H__ */
 /*
-- 
2.23.0


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Re: [Xen-devel] [PATCH for-4.13] x86/passthrough: fix migration of MSI when using posted interrupts

Posted by Jan Beulich 1 week ago
On 09.10.2019 11:05, Roger Pau Monne wrote:
> @@ -411,6 +411,7 @@ int pt_irq_create_bind(
>  
>                  pirq_dpci->gmsi.gvec = pt_irq_bind->u.msi.gvec;
>                  pirq_dpci->gmsi.gflags = gflags;
> +                prev_vcpu_id = pirq_dpci->gmsi.dest_vcpu_id;

If this and ...

> @@ -440,7 +441,8 @@ int pt_irq_create_bind(
>          /* Use interrupt posting if it is supported. */
>          if ( iommu_intpost )
>              pi_update_irte(vcpu ? &vcpu->arch.hvm.vmx.pi_desc : NULL,
> -                           info, pirq_dpci->gmsi.gvec);
> +                           info, pirq_dpci->gmsi.gvec,
> +                           prev_vcpu_id >= 0 ? d->vcpu[prev_vcpu_id] : NULL);

... this are to be reliable, then - as explained to Joe already
in the earlier discussion - I think you need to update
pirq_dpci->gmsi.dest_vcpu_id in a code section a few lines up
from here (such that it would be reliable the next time we come
here) like this:

@@ -xxx,7 +yyy,10 @@
                 vcpu = vector_hashing_dest(d, dest, dest_mode,
                                            pirq_dpci->gmsi.gvec);
             if ( vcpu )
+            {
                 pirq_dpci->gmsi.posted = true;
+                pirq_dpci->gmsi.dest_vcpu_id = vcpu->vcpu_id;
+            }
         }
         if ( vcpu && is_iommu_enabled(d) )
             hvm_migrate_pirq(pirq_dpci, vcpu);

This ought to be fine because so far .dest_vcpu_id has a consumer
only in the non-posted case (in hvm_migrate_pirq()).

Considering that hvm_girq_dest_2_vcpu_id() isn't really inexpensive,
subsequent cleanup may then involve avoiding to call this function
if we'd overwrite .dest_vcpu_id as per above anyway.

> --- a/xen/drivers/passthrough/vtd/intremap.c
> +++ b/xen/drivers/passthrough/vtd/intremap.c
> @@ -946,12 +946,13 @@ void intel_iommu_disable_eim(void)
>          disable_qinval(drhd->iommu);
>  }
>  
> +#if CONFIG_HVM

#ifdef please.

Jan

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Re: [Xen-devel] [PATCH for-4.13] x86/passthrough: fix migration of MSI when using posted interrupts

Posted by Roger Pau Monné 1 week ago
On Wed, Oct 09, 2019 at 12:08:50PM +0200, Jan Beulich wrote:
> On 09.10.2019 11:05, Roger Pau Monne wrote:
> > @@ -411,6 +411,7 @@ int pt_irq_create_bind(
> >  
> >                  pirq_dpci->gmsi.gvec = pt_irq_bind->u.msi.gvec;
> >                  pirq_dpci->gmsi.gflags = gflags;
> > +                prev_vcpu_id = pirq_dpci->gmsi.dest_vcpu_id;
> 
> If this and ...
> 
> > @@ -440,7 +441,8 @@ int pt_irq_create_bind(
> >          /* Use interrupt posting if it is supported. */
> >          if ( iommu_intpost )
> >              pi_update_irte(vcpu ? &vcpu->arch.hvm.vmx.pi_desc : NULL,
> > -                           info, pirq_dpci->gmsi.gvec);
> > +                           info, pirq_dpci->gmsi.gvec,
> > +                           prev_vcpu_id >= 0 ? d->vcpu[prev_vcpu_id] : NULL);
> 
> ... this are to be reliable, then - as explained to Joe already
> in the earlier discussion - I think you need to update
> pirq_dpci->gmsi.dest_vcpu_id in a code section a few lines up
> from here (such that it would be reliable the next time we come
> here) like this:
> 
> @@ -xxx,7 +yyy,10 @@
>                  vcpu = vector_hashing_dest(d, dest, dest_mode,
>                                             pirq_dpci->gmsi.gvec);
>              if ( vcpu )
> +            {
>                  pirq_dpci->gmsi.posted = true;
> +                pirq_dpci->gmsi.dest_vcpu_id = vcpu->vcpu_id;
> +            }
>          }
>          if ( vcpu && is_iommu_enabled(d) )
>              hvm_migrate_pirq(pirq_dpci, vcpu);
> 
> This ought to be fine because so far .dest_vcpu_id has a consumer
> only in the non-posted case (in hvm_migrate_pirq()).

Oh, I see. dest_vcpu_id is only valid for non-multidest, but when
using posted interrupts Xen selects a fixed destination vcpu even in
multidest, so we can take advantage of posted interrupts at the price
of always delivering to the same vcpu.

> 
> Considering that hvm_girq_dest_2_vcpu_id() isn't really inexpensive,
> subsequent cleanup may then involve avoiding to call this function
> if we'd overwrite .dest_vcpu_id as per above anyway.

Hm, I see. I would leave that for a further optimization.

Thanks, Roger.

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Re: [Xen-devel] [PATCH for-4.13] x86/passthrough: fix migration of MSI when using posted interrupts

Posted by Jan Beulich 1 week ago
On 09.10.2019 12:20, Roger Pau Monné  wrote:
> On Wed, Oct 09, 2019 at 12:08:50PM +0200, Jan Beulich wrote:
>> Considering that hvm_girq_dest_2_vcpu_id() isn't really inexpensive,
>> subsequent cleanup may then involve avoiding to call this function
>> if we'd overwrite .dest_vcpu_id as per above anyway.
> 
> Hm, I see. I would leave that for a further optimization.

Sure, hence me saying "subsequent cleanup".

Jan

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