[PATCH v2 0/6] KVM: Fix dirty-ring ordering on weakly ordered architectures

[PATCH v2 0/6] KVM: Fix dirty-ring ordering on weakly ordered architectures

[Marc Zyngier]

[Same distribution list as Gavin's dirty-ring on arm64 series]

This is an update on the initial series posted as [0].

As Gavin started posting patches enabling the dirty-ring infrastructure
on arm64 [1], it quickly became apparent that the API was never intended
to work on relaxed memory ordering architectures (owing to its x86
origins).

This series tries to retrofit some ordering into the existing API by:

- relying on acquire/release semantics which are the default on x86,
  but need to be explicit on arm64

- adding a new capability that indicate which flavor is supported, either
  with explicit ordering (arm64) or both implicit and explicit (x86),
  as suggested by Paolo at KVM Forum

- documenting the requirements for this new capability on weakly ordered
  architectures

- updating the selftests to do the right thing

Ideally, this series should be a prefix of Gavin's, plus a small change
to his series:

diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
index 0309b2d0f2da..7785379c5048 100644
--- a/arch/arm64/kvm/Kconfig
+++ b/arch/arm64/kvm/Kconfig
@@ -32,7 +32,7 @@ menuconfig KVM
 	select KVM_VFIO
 	select HAVE_KVM_EVENTFD
 	select HAVE_KVM_IRQFD
-	select HAVE_KVM_DIRTY_RING
+	select HAVE_KVM_DIRTY_RING_ACQ_REL
 	select HAVE_KVM_MSI
 	select HAVE_KVM_IRQCHIP
 	select HAVE_KVM_IRQ_ROUTING

This has been very lightly tested on an arm64 box with Gavin's v3 [2] series.

* From v1:
  - Repainted the config symbols and new capability so that their
    naming is more acceptable and causes less churn
  - Fixed a couple of blunders as pointed out by Peter and Paolo
  - Updated the documentation

[0] https://lore.kernel.org/r/20220922170133.2617189-1-maz@kernel.org
[1] https://lore.kernel.org/lkml/YyiV%2Fl7O23aw5aaO@xz-m1.local/T/
[2] https://lore.kernel.org/r/20220922003214.276736-1-gshan@redhat.com

Marc Zyngier (6):
  KVM: Use acquire/release semantics when accessing dirty ring GFN state
  KVM: Add KVM_CAP_DIRTY_LOG_RING_ACQ_REL capability and config option
  KVM: x86: Select CONFIG_HAVE_KVM_DIRTY_RING_ACQ_REL
  KVM: Document weakly ordered architecture requirements for dirty ring
  KVM: selftests: dirty-log: Upgrade flag accesses to acquire/release
    semantics
  KVM: selftests: dirty-log: Use KVM_CAP_DIRTY_LOG_RING_ACQ_REL if
    available

 Documentation/virt/kvm/api.rst               | 17 +++++++++++++++--
 arch/x86/kvm/Kconfig                         |  3 ++-
 include/uapi/linux/kvm.h                     |  1 +
 tools/testing/selftests/kvm/dirty_log_test.c |  8 +++++---
 tools/testing/selftests/kvm/lib/kvm_util.c   |  5 ++++-
 virt/kvm/Kconfig                             | 14 ++++++++++++++
 virt/kvm/dirty_ring.c                        |  4 ++--
 virt/kvm/kvm_main.c                          |  9 ++++++++-
 8 files changed, 51 insertions(+), 10 deletions(-)

-- 
2.34.1

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[PATCH v2 1/6] KVM: Use acquire/release semantics when accessing dirty ring GFN state

[Marc Zyngier]

The current implementation of the dirty ring has an implicit requirement
that stores to the dirty ring from userspace must be:

- be ordered with one another

- visible from another CPU executing a ring reset

While these implicit requirements work well for x86 (and any other
TSO-like architecture), they do not work for more relaxed architectures
such as arm64 where stores to different addresses can be freely
reordered, and loads from these addresses not observing writes from
another CPU unless the required barriers (or acquire/release semantics)
are used.

In order to start fixing this, upgrade the ring reset accesses:

- the kvm_dirty_gfn_harvested() helper now uses acquire semantics
  so it is ordered after all previous writes, including that from
  userspace

- the kvm_dirty_gfn_set_invalid() helper now uses release semantics
  so that the next_slot and next_offset reads don't drift past
  the entry invalidation

This is only a partial fix as the userspace side also need upgrading.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 virt/kvm/dirty_ring.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/dirty_ring.c b/virt/kvm/dirty_ring.c
index f4c2a6eb1666..d6fabf238032 100644
--- a/virt/kvm/dirty_ring.c
+++ b/virt/kvm/dirty_ring.c
@@ -74,7 +74,7 @@ int kvm_dirty_ring_alloc(struct kvm_dirty_ring *ring, int index, u32 size)
 
 static inline void kvm_dirty_gfn_set_invalid(struct kvm_dirty_gfn *gfn)
 {
-	gfn->flags = 0;
+	smp_store_release(&gfn->flags, 0);
 }
 
 static inline void kvm_dirty_gfn_set_dirtied(struct kvm_dirty_gfn *gfn)
@@ -84,7 +84,7 @@ static inline void kvm_dirty_gfn_set_dirtied(struct kvm_dirty_gfn *gfn)
 
 static inline bool kvm_dirty_gfn_harvested(struct kvm_dirty_gfn *gfn)
 {
-	return gfn->flags & KVM_DIRTY_GFN_F_RESET;
+	return smp_load_acquire(&gfn->flags) & KVM_DIRTY_GFN_F_RESET;
 }
 
 int kvm_dirty_ring_reset(struct kvm *kvm, struct kvm_dirty_ring *ring)
-- 
2.34.1

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[PATCH v2 2/6] KVM: Add KVM_CAP_DIRTY_LOG_RING_ACQ_REL capability and config option

[Marc Zyngier]

In order to differenciate between architectures that require no extra
synchronisation when accessing the dirty ring and those who do,
add a new capability (KVM_CAP_DIRTY_LOG_RING_ACQ_REL) that identify
the latter sort. TSO architectures can obviously advertise both, while
relaxed architectures must only advertise the ACQ_REL version.

This requires some configuration symbol rejigging, with HAVE_KVM_DIRTY_RING
being only indirectly selected by two top-level config symbols:
- HAVE_KVM_DIRTY_RING_TSO for strongly ordered architectures (x86)
- HAVE_KVM_DIRTY_RING_ACQ_REL for weakly ordered architectures (arm64)

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/x86/kvm/Kconfig     |  2 +-
 include/uapi/linux/kvm.h |  1 +
 virt/kvm/Kconfig         | 14 ++++++++++++++
 virt/kvm/kvm_main.c      |  9 ++++++++-
 4 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index e3cbd7706136..876748b236ff 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -28,7 +28,7 @@ config KVM
 	select HAVE_KVM_IRQCHIP
 	select HAVE_KVM_PFNCACHE
 	select HAVE_KVM_IRQFD
-	select HAVE_KVM_DIRTY_RING
+	select HAVE_KVM_DIRTY_RING_TSO
 	select IRQ_BYPASS_MANAGER
 	select HAVE_KVM_IRQ_BYPASS
 	select HAVE_KVM_IRQ_ROUTING
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index eed0315a77a6..0d5d4419139a 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1177,6 +1177,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_VM_DISABLE_NX_HUGE_PAGES 220
 #define KVM_CAP_S390_ZPCI_OP 221
 #define KVM_CAP_S390_CPU_TOPOLOGY 222
+#define KVM_CAP_DIRTY_LOG_RING_ACQ_REL 223
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
index a8c5c9f06b3c..800f9470e36b 100644
--- a/virt/kvm/Kconfig
+++ b/virt/kvm/Kconfig
@@ -19,6 +19,20 @@ config HAVE_KVM_IRQ_ROUTING
 config HAVE_KVM_DIRTY_RING
        bool
 
+# Only strongly ordered architectures can select this, as it doesn't
+# put any explicit constraint on userspace ordering. They can also
+# select the _ACQ_REL version.
+config HAVE_KVM_DIRTY_RING_TSO
+       bool
+       select HAVE_KVM_DIRTY_RING
+       depends on X86
+
+# Weakly ordered architectures can only select this, advertising
+# to userspace the additional ordering requirements.
+config HAVE_KVM_DIRTY_RING_ACQ_REL
+       bool
+       select HAVE_KVM_DIRTY_RING
+
 config HAVE_KVM_EVENTFD
        bool
        select EVENTFD
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 584a5bab3af3..5b064dbadaf4 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4475,7 +4475,13 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
 	case KVM_CAP_NR_MEMSLOTS:
 		return KVM_USER_MEM_SLOTS;
 	case KVM_CAP_DIRTY_LOG_RING:
-#ifdef CONFIG_HAVE_KVM_DIRTY_RING
+#ifdef CONFIG_HAVE_KVM_DIRTY_RING_TSO
+		return KVM_DIRTY_RING_MAX_ENTRIES * sizeof(struct kvm_dirty_gfn);
+#else
+		return 0;
+#endif
+	case KVM_CAP_DIRTY_LOG_RING_ACQ_REL:
+#ifdef CONFIG_HAVE_KVM_DIRTY_RING_ACQ_REL
 		return KVM_DIRTY_RING_MAX_ENTRIES * sizeof(struct kvm_dirty_gfn);
 #else
 		return 0;
@@ -4580,6 +4586,7 @@ static int kvm_vm_ioctl_enable_cap_generic(struct kvm *kvm,
 		return 0;
 	}
 	case KVM_CAP_DIRTY_LOG_RING:
+	case KVM_CAP_DIRTY_LOG_RING_ACQ_REL:
 		return kvm_vm_ioctl_enable_dirty_log_ring(kvm, cap->args[0]);
 	default:
 		return kvm_vm_ioctl_enable_cap(kvm, cap);
-- 
2.34.1

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[PATCH v2 3/6] KVM: x86: Select CONFIG_HAVE_KVM_DIRTY_RING_ACQ_REL

[Marc Zyngier]

Since x86 is TSO (give or take), allow it to advertise the new
ACQ_REL version of the dirty ring capability. No other change is
required for it.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/x86/kvm/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 876748b236ff..67be7f217e37 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -29,6 +29,7 @@ config KVM
 	select HAVE_KVM_PFNCACHE
 	select HAVE_KVM_IRQFD
 	select HAVE_KVM_DIRTY_RING_TSO
+	select HAVE_KVM_DIRTY_RING_ACQ_REL
 	select IRQ_BYPASS_MANAGER
 	select HAVE_KVM_IRQ_BYPASS
 	select HAVE_KVM_IRQ_ROUTING
-- 
2.34.1

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[PATCH v2 4/6] KVM: Document weakly ordered architecture requirements for dirty ring

[Marc Zyngier]

Now that the kernel can expose to userspace that its dirty ring
management relies on explicit ordering, document these new requirements
for VMMs to do the right thing.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 Documentation/virt/kvm/api.rst | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index abd7c32126ce..32427ea160df 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -8019,8 +8019,8 @@ guest according to the bits in the KVM_CPUID_FEATURES CPUID leaf
 (0x40000001). Otherwise, a guest may use the paravirtual features
 regardless of what has actually been exposed through the CPUID leaf.
 
-8.29 KVM_CAP_DIRTY_LOG_RING
----------------------------
+8.29 KVM_CAP_DIRTY_LOG_RING/KVM_CAP_DIRTY_LOG_RING_ACQ_REL
+----------------------------------------------------------
 
 :Architectures: x86
 :Parameters: args[0] - size of the dirty log ring
@@ -8078,6 +8078,11 @@ on to the next GFN.  The userspace should continue to do this until the
 flags of a GFN have the DIRTY bit cleared, meaning that it has harvested
 all the dirty GFNs that were available.
 
+Note that on weakly ordered architectures, userspace accesses to the
+ring buffer (and more specifically the 'flags' field) must be ordered,
+using load-acquire/store-release accessors when available, or any
+other memory barrier that will ensure this ordering.
+
 It's not necessary for userspace to harvest the all dirty GFNs at once.
 However it must collect the dirty GFNs in sequence, i.e., the userspace
 program cannot skip one dirty GFN to collect the one next to it.
@@ -8106,6 +8111,14 @@ KVM_CAP_DIRTY_LOG_RING with an acceptable dirty ring size, the virtual
 machine will switch to ring-buffer dirty page tracking and further
 KVM_GET_DIRTY_LOG or KVM_CLEAR_DIRTY_LOG ioctls will fail.
 
+NOTE: KVM_CAP_DIRTY_LOG_RING_ACQ_REL is the only capability that
+should be exposed by weakly ordered architecture, in order to indicate
+the additional memory ordering requirements imposed on userspace when
+reading the state of an entry and mutating it from DIRTY to HARVESTED.
+Architecture with TSO-like ordering (such as x86) are allowed to
+expose both KVM_CAP_DIRTY_LOG_RING and KVM_CAP_DIRTY_LOG_RING_ACQ_REL
+to userspace.
+
 8.30 KVM_CAP_XEN_HVM
 --------------------
 
-- 
2.34.1

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[PATCH v2 5/6] KVM: selftests: dirty-log: Upgrade flag accesses to acquire/release semantics

[Marc Zyngier]

In order to preserve ordering, make sure that the flag accesses
in the dirty log are done using acquire/release accessors.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 tools/testing/selftests/kvm/dirty_log_test.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c
index 9c883c94d478..53627add8a7c 100644
--- a/tools/testing/selftests/kvm/dirty_log_test.c
+++ b/tools/testing/selftests/kvm/dirty_log_test.c
@@ -17,6 +17,7 @@
 #include <linux/bitmap.h>
 #include <linux/bitops.h>
 #include <linux/atomic.h>
+#include <asm/barrier.h>
 
 #include "kvm_util.h"
 #include "test_util.h"
@@ -279,12 +280,12 @@ static void dirty_ring_create_vm_done(struct kvm_vm *vm)
 
 static inline bool dirty_gfn_is_dirtied(struct kvm_dirty_gfn *gfn)
 {
-	return gfn->flags == KVM_DIRTY_GFN_F_DIRTY;
+	return smp_load_acquire(&gfn->flags) == KVM_DIRTY_GFN_F_DIRTY;
 }
 
 static inline void dirty_gfn_set_collected(struct kvm_dirty_gfn *gfn)
 {
-	gfn->flags = KVM_DIRTY_GFN_F_RESET;
+	smp_store_release(&gfn->flags, KVM_DIRTY_GFN_F_RESET);
 }
 
 static uint32_t dirty_ring_collect_one(struct kvm_dirty_gfn *dirty_gfns,
-- 
2.34.1

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[PATCH v2 6/6] KVM: selftests: dirty-log: Use KVM_CAP_DIRTY_LOG_RING_ACQ_REL if available

[Marc Zyngier]

Pick KVM_CAP_DIRTY_LOG_RING_ACQ_REL if exposed by the kernel.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 tools/testing/selftests/kvm/dirty_log_test.c | 3 ++-
 tools/testing/selftests/kvm/lib/kvm_util.c   | 5 ++++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c
index 53627add8a7c..b5234d6efbe1 100644
--- a/tools/testing/selftests/kvm/dirty_log_test.c
+++ b/tools/testing/selftests/kvm/dirty_log_test.c
@@ -265,7 +265,8 @@ static void default_after_vcpu_run(struct kvm_vcpu *vcpu, int ret, int err)
 
 static bool dirty_ring_supported(void)
 {
-	return kvm_has_cap(KVM_CAP_DIRTY_LOG_RING);
+	return (kvm_has_cap(KVM_CAP_DIRTY_LOG_RING) ||
+		kvm_has_cap(KVM_CAP_DIRTY_LOG_RING_ACQ_REL));
 }
 
 static void dirty_ring_create_vm_done(struct kvm_vm *vm)
diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index 9889fe0d8919..411a4c0bc81c 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -82,7 +82,10 @@ unsigned int kvm_check_cap(long cap)
 
 void vm_enable_dirty_ring(struct kvm_vm *vm, uint32_t ring_size)
 {
-	vm_enable_cap(vm, KVM_CAP_DIRTY_LOG_RING, ring_size);
+	if (vm_check_cap(vm, KVM_CAP_DIRTY_LOG_RING_ACQ_REL))
+		vm_enable_cap(vm, KVM_CAP_DIRTY_LOG_RING_ACQ_REL, ring_size);
+	else
+		vm_enable_cap(vm, KVM_CAP_DIRTY_LOG_RING, ring_size);
 	vm->dirty_ring_size = ring_size;
 }
 
-- 
2.34.1

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Re: [PATCH v2 0/6] KVM: Fix dirty-ring ordering on weakly ordered architectures

[Gavin Shan]

On 9/27/22 12:51 AM, Marc Zyngier wrote:
> [Same distribution list as Gavin's dirty-ring on arm64 series]
> 
> This is an update on the initial series posted as [0].
> 
> As Gavin started posting patches enabling the dirty-ring infrastructure
> on arm64 [1], it quickly became apparent that the API was never intended
> to work on relaxed memory ordering architectures (owing to its x86
> origins).
> 
> This series tries to retrofit some ordering into the existing API by:
> 
> - relying on acquire/release semantics which are the default on x86,
>    but need to be explicit on arm64
> 
> - adding a new capability that indicate which flavor is supported, either
>    with explicit ordering (arm64) or both implicit and explicit (x86),
>    as suggested by Paolo at KVM Forum
> 
> - documenting the requirements for this new capability on weakly ordered
>    architectures
> 
> - updating the selftests to do the right thing
> 
> Ideally, this series should be a prefix of Gavin's, plus a small change
> to his series:
> 
> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> index 0309b2d0f2da..7785379c5048 100644
> --- a/arch/arm64/kvm/Kconfig
> +++ b/arch/arm64/kvm/Kconfig
> @@ -32,7 +32,7 @@ menuconfig KVM
>   	select KVM_VFIO
>   	select HAVE_KVM_EVENTFD
>   	select HAVE_KVM_IRQFD
> -	select HAVE_KVM_DIRTY_RING
> +	select HAVE_KVM_DIRTY_RING_ACQ_REL
>   	select HAVE_KVM_MSI
>   	select HAVE_KVM_IRQCHIP
>   	select HAVE_KVM_IRQ_ROUTING
> 
> This has been very lightly tested on an arm64 box with Gavin's v3 [2] series.
> 
> * From v1:
>    - Repainted the config symbols and new capability so that their
>      naming is more acceptable and causes less churn
>    - Fixed a couple of blunders as pointed out by Peter and Paolo
>    - Updated the documentation
> 
> [0] https://lore.kernel.org/r/20220922170133.2617189-1-maz@kernel.org
> [1] https://lore.kernel.org/lkml/YyiV%2Fl7O23aw5aaO@xz-m1.local/T/
> [2] https://lore.kernel.org/r/20220922003214.276736-1-gshan@redhat.com
> 
> Marc Zyngier (6):
>    KVM: Use acquire/release semantics when accessing dirty ring GFN state
>    KVM: Add KVM_CAP_DIRTY_LOG_RING_ACQ_REL capability and config option
>    KVM: x86: Select CONFIG_HAVE_KVM_DIRTY_RING_ACQ_REL
>    KVM: Document weakly ordered architecture requirements for dirty ring
>    KVM: selftests: dirty-log: Upgrade flag accesses to acquire/release
>      semantics
>    KVM: selftests: dirty-log: Use KVM_CAP_DIRTY_LOG_RING_ACQ_REL if
>      available
> 
>   Documentation/virt/kvm/api.rst               | 17 +++++++++++++++--
>   arch/x86/kvm/Kconfig                         |  3 ++-
>   include/uapi/linux/kvm.h                     |  1 +
>   tools/testing/selftests/kvm/dirty_log_test.c |  8 +++++---
>   tools/testing/selftests/kvm/lib/kvm_util.c   |  5 ++++-
>   virt/kvm/Kconfig                             | 14 ++++++++++++++
>   virt/kvm/dirty_ring.c                        |  4 ++--
>   virt/kvm/kvm_main.c                          |  9 ++++++++-
>   8 files changed, 51 insertions(+), 10 deletions(-)
> 

This series looks good to me.

Reviewed-by: Gavin Shan <gshan@redhat.com>

Thanks,
Gavin

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Re: [PATCH v2 0/6] KVM: Fix dirty-ring ordering on weakly ordered architectures

[Peter Xu]

On Mon, Sep 26, 2022 at 03:51:14PM +0100, Marc Zyngier wrote:
> [Same distribution list as Gavin's dirty-ring on arm64 series]
> 
> This is an update on the initial series posted as [0].
> 
> As Gavin started posting patches enabling the dirty-ring infrastructure
> on arm64 [1], it quickly became apparent that the API was never intended
> to work on relaxed memory ordering architectures (owing to its x86
> origins).
> 
> This series tries to retrofit some ordering into the existing API by:
> 
> - relying on acquire/release semantics which are the default on x86,
>   but need to be explicit on arm64
> 
> - adding a new capability that indicate which flavor is supported, either
>   with explicit ordering (arm64) or both implicit and explicit (x86),
>   as suggested by Paolo at KVM Forum
> 
> - documenting the requirements for this new capability on weakly ordered
>   architectures
> 
> - updating the selftests to do the right thing
> 
> Ideally, this series should be a prefix of Gavin's, plus a small change
> to his series:
> 
> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> index 0309b2d0f2da..7785379c5048 100644
> --- a/arch/arm64/kvm/Kconfig
> +++ b/arch/arm64/kvm/Kconfig
> @@ -32,7 +32,7 @@ menuconfig KVM
>  	select KVM_VFIO
>  	select HAVE_KVM_EVENTFD
>  	select HAVE_KVM_IRQFD
> -	select HAVE_KVM_DIRTY_RING
> +	select HAVE_KVM_DIRTY_RING_ACQ_REL
>  	select HAVE_KVM_MSI
>  	select HAVE_KVM_IRQCHIP
>  	select HAVE_KVM_IRQ_ROUTING
> 
> This has been very lightly tested on an arm64 box with Gavin's v3 [2] series.
> 
> * From v1:
>   - Repainted the config symbols and new capability so that their
>     naming is more acceptable and causes less churn
>   - Fixed a couple of blunders as pointed out by Peter and Paolo
>   - Updated the documentation
> 
> [0] https://lore.kernel.org/r/20220922170133.2617189-1-maz@kernel.org
> [1] https://lore.kernel.org/lkml/YyiV%2Fl7O23aw5aaO@xz-m1.local/T/
> [2] https://lore.kernel.org/r/20220922003214.276736-1-gshan@redhat.com
> 
> Marc Zyngier (6):
>   KVM: Use acquire/release semantics when accessing dirty ring GFN state
>   KVM: Add KVM_CAP_DIRTY_LOG_RING_ACQ_REL capability and config option
>   KVM: x86: Select CONFIG_HAVE_KVM_DIRTY_RING_ACQ_REL
>   KVM: Document weakly ordered architecture requirements for dirty ring
>   KVM: selftests: dirty-log: Upgrade flag accesses to acquire/release
>     semantics
>   KVM: selftests: dirty-log: Use KVM_CAP_DIRTY_LOG_RING_ACQ_REL if
>     available

Reviewed-by: Peter Xu <peterx@redhat.com>

Thanks!

-- 
Peter Xu

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Re: [PATCH v2 0/6] KVM: Fix dirty-ring ordering on weakly ordered architectures

[Marc Zyngier]

On Mon, 26 Sep 2022 15:51:14 +0100, Marc Zyngier wrote:
> [Same distribution list as Gavin's dirty-ring on arm64 series]
> 
> This is an update on the initial series posted as [0].
> 
> As Gavin started posting patches enabling the dirty-ring infrastructure
> on arm64 [1], it quickly became apparent that the API was never intended
> to work on relaxed memory ordering architectures (owing to its x86
> origins).
> 
> [...]

Applied to next, thanks!

[1/6] KVM: Use acquire/release semantics when accessing dirty ring GFN state
      commit: 8929bc9659640f35dd2ef8373263cbd885b4a072
[2/6] KVM: Add KVM_CAP_DIRTY_LOG_RING_ACQ_REL capability and config option
      commit: 17601bfed909fa080fcfd227b57da2bd4dc2d2a6
[3/6] KVM: x86: Select CONFIG_HAVE_KVM_DIRTY_RING_ACQ_REL
      commit: fc0693d4e5afe3c110503c3afa9f60600f9e964b
[4/6] KVM: Document weakly ordered architecture requirements for dirty ring
      commit: 671c8c7f9f2349d8b2176ad810f1406794011f63
[5/6] KVM: selftests: dirty-log: Upgrade flag accesses to acquire/release semantics
      commit: 4eb6486cb43c93382c27a2659ba978c660e98498
[6/6] KVM: selftests: dirty-log: Use KVM_CAP_DIRTY_LOG_RING_ACQ_REL if available
      commit: 4b3402f1f4d9860301d6d5cd7aff3b67f678d577

Cheers,

	M.
-- 
Without deviation from the norm, progress is not possible.


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