[PATCH] iommu/vt-d: Use cmpxchg16b to update posted format IRTE atomically

[PATCH] iommu/vt-d: Use cmpxchg16b to update posted format IRTE atomically

[Feng Wu]

If IRTE is in posted format, the 'pda' field goes across the 64-bit
boundary, we need use cmpxchg16b to atomically update it. We only
expose posted-interrupt when X86_FEATURE_CX16 is supported and use
to update it atomically.

Signed-off-by: Feng Wu <feng.wu-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
---
 drivers/iommu/intel_irq_remapping.c | 33 ++++++++++++++++++++++++++++++---
 1 file changed, 30 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/intel_irq_remapping.c b/drivers/iommu/intel_irq_remapping.c
index f15692a..b4f7569 100644
--- a/drivers/iommu/intel_irq_remapping.c
+++ b/drivers/iommu/intel_irq_remapping.c
@@ -169,8 +169,26 @@ static int modify_irte(struct irq_2_iommu *irq_iommu,
 	index = irq_iommu->irte_index + irq_iommu->sub_handle;
 	irte = &iommu->ir_table->base[index];
 
-	set_64bit(&irte->low, irte_modified->low);
-	set_64bit(&irte->high, irte_modified->high);
+#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE)
+	if ((irte->pst == 1) || (irte_modified->pst == 1)) {
+		bool ret;
+
+		ret = cmpxchg_double(&irte->low, &irte->high,
+				     irte->low, irte->high,
+				     irte_modified->low, irte_modified->high);
+		/*
+		 * We use cmpxchg16 to atomically update the 128-bit IRTE,
+		 * and it cannot be updated by the hardware or other processors
+		 * behind us, so the return value of cmpxchg16 should be the
+		 * same as the old value.
+		 */
+		BUG_ON(!ret);
+	} else
+#endif
+	{
+		set_64bit(&irte->low, irte_modified->low);
+		set_64bit(&irte->high, irte_modified->high);
+	}
 	__iommu_flush_cache(iommu, irte, sizeof(*irte));
 
 	rc = qi_flush_iec(iommu, index, 0);
@@ -725,7 +743,16 @@ static inline void set_irq_posting_cap(void)
 	struct intel_iommu *iommu;
 
 	if (!disable_irq_post) {
-		intel_irq_remap_ops.capability |= 1 << IRQ_POSTING_CAP;
+		/*
+		 * If IRTE is in posted format, the 'pda' field goes across the
+		 * 64-bit boundary, we need use cmpxchg16b to atomically update
+		 * it. We only expose posted-interrupt when X86_FEATURE_CX16
+		 * is supported. Actually, hardware platforms supporting PI
+		 * should have X86_FEATURE_CX16 support, this has been confirmed
+		 * with Intel hardware guys.
+		 */
+		if ( cpu_has_cx16 )
+			intel_irq_remap_ops.capability |= 1 << IRQ_POSTING_CAP;
 
 		for_each_iommu(iommu, drhd)
 			if (!cap_pi_support(iommu->cap)) {
-- 
2.1.0

Re: [PATCH] iommu/vt-d: Use cmpxchg16b to update posted format IRTE atomically

[Joerg Roedel]

On Thu, Oct 15, 2015 at 10:19:11AM +0800, Feng Wu wrote:
> If IRTE is in posted format, the 'pda' field goes across the 64-bit
> boundary, we need use cmpxchg16b to atomically update it. We only
> expose posted-interrupt when X86_FEATURE_CX16 is supported and use
> to update it atomically.
> 
> Signed-off-by: Feng Wu <feng.wu-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
> ---
>  drivers/iommu/intel_irq_remapping.c | 33 ++++++++++++++++++++++++++++++---
>  1 file changed, 30 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iommu/intel_irq_remapping.c b/drivers/iommu/intel_irq_remapping.c
> index f15692a..b4f7569 100644
> --- a/drivers/iommu/intel_irq_remapping.c
> +++ b/drivers/iommu/intel_irq_remapping.c
> @@ -169,8 +169,26 @@ static int modify_irte(struct irq_2_iommu *irq_iommu,
>  	index = irq_iommu->irte_index + irq_iommu->sub_handle;
>  	irte = &iommu->ir_table->base[index];
>  
> -	set_64bit(&irte->low, irte_modified->low);
> -	set_64bit(&irte->high, irte_modified->high);
> +#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE)
> +	if ((irte->pst == 1) || (irte_modified->pst == 1)) {
> +		bool ret;
> +
> +		ret = cmpxchg_double(&irte->low, &irte->high,
> +				     irte->low, irte->high,
> +				     irte_modified->low, irte_modified->high);
> +		/*
> +		 * We use cmpxchg16 to atomically update the 128-bit IRTE,
> +		 * and it cannot be updated by the hardware or other processors
> +		 * behind us, so the return value of cmpxchg16 should be the
> +		 * same as the old value.
> +		 */
> +		BUG_ON(!ret);

Changed this to a WARN_ON, otherwise applied.

RE: [PATCH] iommu/vt-d: Use cmpxchg16b to update posted format IRTE atomically

[Wu, Feng]

> -----Original Message-----
> From: linux-kernel-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org [mailto:linux-kernel-
> owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org] On Behalf Of Joerg Roedel
> Sent: Thursday, October 15, 2015 10:24 PM
> To: Wu, Feng <feng.wu-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
> Cc: iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org; linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> Subject: Re: [PATCH] iommu/vt-d: Use cmpxchg16b to update posted format
> IRTE atomically
> 
> On Thu, Oct 15, 2015 at 10:19:11AM +0800, Feng Wu wrote:
> > If IRTE is in posted format, the 'pda' field goes across the 64-bit
> > boundary, we need use cmpxchg16b to atomically update it. We only
> > expose posted-interrupt when X86_FEATURE_CX16 is supported and use
> > to update it atomically.
> > +
> > +		ret = cmpxchg_double(&irte->low, &irte->high,
> > +				     irte->low, irte->high,
> > +				     irte_modified->low, irte_modified->high);
> > +		/*
> > +		 * We use cmpxchg16 to atomically update the 128-bit IRTE,
> > +		 * and it cannot be updated by the hardware or other
> processors
> > +		 * behind us, so the return value of cmpxchg16 should be the
> > +		 * same as the old value.
> > +		 */
> > +		BUG_ON(!ret);
> 
> Changed this to a WARN_ON, otherwise applied.

Thanks a lot, Joerg!

Thanks,
Feng