2022-12-19 15:46:32

by Peter Zijlstra

Subject: [RFC][PATCH 09/12] x86,amd_iommu: Replace cmpxchg_double()

Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
---
drivers/iommu/amd/amd_iommu_types.h | 9 +++++++--
drivers/iommu/amd/iommu.c | 10 ++++------
2 files changed, 11 insertions(+), 8 deletions(-)

--- a/drivers/iommu/amd/amd_iommu_types.h
+++ b/drivers/iommu/amd/amd_iommu_types.h
@@ -979,8 +979,13 @@ union irte_ga_hi {
};

struct irte_ga {
- union irte_ga_lo lo;
- union irte_ga_hi hi;
+ union {
+ struct {
+ union irte_ga_lo lo;
+ union irte_ga_hi hi;
+ };
+ u128 irte;
+ };
};

struct irq_2_irte {
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -2992,10 +2992,10 @@ static int alloc_irq_index(struct amd_io
static int modify_irte_ga(struct amd_iommu *iommu, u16 devid, int index,
struct irte_ga *irte, struct amd_ir_data *data)
{
- bool ret;
struct irq_remap_table *table;
- unsigned long flags;
struct irte_ga *entry;
+ unsigned long flags;
+ u128 old;

table = get_irq_table(iommu, devid);
if (!table)
@@ -3006,16 +3006,14 @@ static int modify_irte_ga(struct amd_iom
entry = (struct irte_ga *)table->table;
entry = &entry[index];

- ret = cmpxchg_double(&entry->lo.val, &entry->hi.val,
- entry->lo.val, entry->hi.val,
- irte->lo.val, irte->hi.val);
/*
* 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.
*/
- WARN_ON(!ret);
+ old = entry->irte;
+ WARN_ON(!try_cmpxchg128(&entry->irte, &old, irte->irte));

if (data)
data->ref = entry;

2022-12-19 16:51:31

by Niklas Schnelle

Subject: Re: [RFC][PATCH 09/12] x86,amd_iommu: Replace cmpxchg_double()

On Mon, 2022-12-19 at 16:35 +0100, Peter Zijlstra wrote:
> Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
> ---
> drivers/iommu/amd/amd_iommu_types.h | 9 +++++++--
> drivers/iommu/amd/iommu.c | 10 ++++------
> 2 files changed, 11 insertions(+), 8 deletions(-)
>
> --- a/drivers/iommu/amd/amd_iommu_types.h
> +++ b/drivers/iommu/amd/amd_iommu_types.h
> @@ -979,8 +979,13 @@ union irte_ga_hi {
> };
>
> struct irte_ga {
> - union irte_ga_lo lo;
> - union irte_ga_hi hi;
> + union {
> + struct {
> + union irte_ga_lo lo;
> + union irte_ga_hi hi;
> + };
> + u128 irte;
> + };
> };
>
> struct irq_2_irte {
> --- a/drivers/iommu/amd/iommu.c
> +++ b/drivers/iommu/amd/iommu.c
> @@ -2992,10 +2992,10 @@ static int alloc_irq_index(struct amd_io
> static int modify_irte_ga(struct amd_iommu *iommu, u16 devid, int index,
> struct irte_ga *irte, struct amd_ir_data *data)
> {
> - bool ret;
> struct irq_remap_table *table;
> - unsigned long flags;
> struct irte_ga *entry;
> + unsigned long flags;
> + u128 old;
>
> table = get_irq_table(iommu, devid);
> if (!table)
> @@ -3006,16 +3006,14 @@ static int modify_irte_ga(struct amd_iom
> entry = (struct irte_ga *)table->table;
> entry = &entry[index];
>
> - ret = cmpxchg_double(&entry->lo.val, &entry->hi.val,
> - entry->lo.val, entry->hi.val,
> - irte->lo.val, irte->hi.val);
> /*
> * 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.

The above comment seems to have already been out of date but could be
updated to say cmpxchg128 instead of cmxchg16 anyway.

> */
> - WARN_ON(!ret);
> + old = entry->irte;
> + WARN_ON(!try_cmpxchg128(&entry->irte, &old, irte->irte));
>
> if (data)
> data->ref = entry;
>
>

2022-12-28 08:42:11

by Vasant Hegde

Subject: Re: [RFC][PATCH 09/12] x86,amd_iommu: Replace cmpxchg_double()

On 12/19/2022 9:05 PM, Peter Zijlstra wrote:
>
> Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
> ---
> drivers/iommu/amd/amd_iommu_types.h | 9 +++++++--
> drivers/iommu/amd/iommu.c | 10 ++++------
> 2 files changed, 11 insertions(+), 8 deletions(-)
>
> --- a/drivers/iommu/amd/amd_iommu_types.h
> +++ b/drivers/iommu/amd/amd_iommu_types.h
> @@ -979,8 +979,13 @@ union irte_ga_hi {
> };
>
> struct irte_ga {
> - union irte_ga_lo lo;
> - union irte_ga_hi hi;
> + union {
> + struct {
> + union irte_ga_lo lo;
> + union irte_ga_hi hi;
> + };
> + u128 irte;
> + };
> };
>
> struct irq_2_irte {
> --- a/drivers/iommu/amd/iommu.c
> +++ b/drivers/iommu/amd/iommu.c
> @@ -2992,10 +2992,10 @@ static int alloc_irq_index(struct amd_io
> static int modify_irte_ga(struct amd_iommu *iommu, u16 devid, int index,
> struct irte_ga *irte, struct amd_ir_data *data)
> {
> - bool ret;
> struct irq_remap_table *table;
> - unsigned long flags;
> struct irte_ga *entry;
> + unsigned long flags;
> + u128 old;
>
> table = get_irq_table(iommu, devid);
> if (!table)
> @@ -3006,16 +3006,14 @@ static int modify_irte_ga(struct amd_iom
> entry = (struct irte_ga *)table->table;
> entry = &entry[index];
>
> - ret = cmpxchg_double(&entry->lo.val, &entry->hi.val,
> - entry->lo.val, entry->hi.val,
> - irte->lo.val, irte->hi.val);
> /*
> * 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.
> */
> - WARN_ON(!ret);
> + old = entry->irte;
> + WARN_ON(!try_cmpxchg128(&entry->irte, &old, irte->irte));

Changes looks good to me. I have tested it on AMD system and it works fine.

-Vasant