Re: [RFC PATCH 19/45] KVM: arm64: iommu: Add domains

Mostafa Saleh
2023-06-15T13:33:10Z

Hi Jean,

On Fri, Jun 02, 2023 at 04:29:07PM +0100, Jean-Philippe Brucker wrote:
> Hi Mostafa,
>
> On Fri, 19 May 2023 at 16:33, Mostafa Saleh <smostafa@google.com> wrote:
> >
> > Hi Jean,
> >
> > On Wed, Feb 01, 2023 at 12:53:03PM +0000, Jean-Philippe Brucker wrote:
> > > +/*
> > > + * Serialize access to domains and IOMMU driver internal structures (command
> > > + * queue, device tables)
> > > + */
> > > +static hyp_spinlock_t iommu_lock;
> > > +
> > I was looking more into this lock and I think we can make it per IOMMU instead
> > of having one big lock to avoid congestion, as I see it is only used to
> > protect per-IOMMU resources.
>
> Yes it's a major bottleneck, thanks for looking into this. I think we'll
> eventually want to improve scalability within an IOMMU and even a domain:
> a multi-queue network device will share a single domain between multiple
> CPUs, each issuing lots of map/unmap calls. Or just two devices drivers
> working on different CPUs and sharing one IOMMU. In those cases the
> per-IOMMU lock won't be good enough and we'll be back to this problem, but
> a per-IOMMU lock should already improve scalability for some systems.
>
> Currently the global lock protects:
>
> (1) The domain array (per IOMMU)
> (2) The io-pgtables (per domain)
> (3) The command queue (per SMMU)
> (4) Power state (per SMMU)
>
> I ran some experiments with refcounting the domains to avoid the lock for
> (1) and (2), which improves map() scalability. See
> https://jpbrucker.net/git/linux/commit/?h=pkvm/smmu-wip&id=5ad3bc6fd589b6f11fe31ccee5b8777ba8739167
> (and another experiment to optimize the DMA refcount on branch pkvm/smmu-wip)

Thanks for the detailed explanation! I will give it a try.

> For (2), the io-pgtable-arm code already supports concurrent accesses
> (2c3d273eabe8 ("iommu/io-pgtable-arm: Support lockless operation")). But
> this one needs careful consideration because in the host, the io-pgtable
> code trusts the device drivers. For example it expects that only buggy
> drivers call map()/unmap() to the same IOVA concurrently. We need to make
> sure a compromised host drivers can't exploit these assumptions to do
> anything nasty.
>
> There are options to improve (3) as well. The host SMMU driver supports
> lockless command-queue (587e6c10a7ce ("iommu/arm-smmu-v3: Reduce
> contention during command-queue insertion")) but it may be too complex to
> put in the hypervisor (or rather, I haven't tried to understand it yet).
> We could also wait for systems with ECMDQ, which enables per-CPU queues.
I was thinking about the same thing, in the futrue we should aim to have a
similar lockless approach for the cmdq as the host in EL2. I am not sure
how feasable it is, I will have a closer look. But having a per-IOMMU
shouldbe be a step in the right direction.

> > Some special handling needed as hyp_spinlock_t is not exposed to EL1.
> > Maybe something like this:
> >
> > diff --git a/arch/arm64/kvm/hyp/hyp-constants.c b/arch/arm64/kvm/hyp/hyp-constants.c
> > index b257a3b4bfc5..96d30a37f9e6 100644
> > --- a/arch/arm64/kvm/hyp/hyp-constants.c
> > +++ b/arch/arm64/kvm/hyp/hyp-constants.c
> > @@ -3,11 +3,13 @@
> > #include <linux/kbuild.h>
> > #include <nvhe/memory.h>
> > #include <nvhe/pkvm.h>
> > +#include <nvhe/spinlock.h>
> >
> > int main(void)
> > {
> > DEFINE(STRUCT_HYP_PAGE_SIZE, sizeof(struct hyp_page));
> > DEFINE(PKVM_HYP_VM_SIZE, sizeof(struct pkvm_hyp_vm));
> > DEFINE(PKVM_HYP_VCPU_SIZE, sizeof(struct pkvm_hyp_vcpu));
> > + DEFINE(HYP_SPINLOCK_SIZE, sizeof(hyp_spinlock_t));
> > return 0;
> > }
> > diff --git a/drivers/iommu/arm/arm-smmu-v3/Makefile b/drivers/iommu/arm/arm-smmu-v3/Makefile
> > index a90b97d8bae3..cf9195e24a08 100644
> > --- a/drivers/iommu/arm/arm-smmu-v3/Makefile
> > +++ b/drivers/iommu/arm/arm-smmu-v3/Makefile
> > @@ -6,6 +6,7 @@ arm_smmu_v3-objs-$(CONFIG_ARM_SMMU_V3_SVA) += arm-smmu-v3-sva.o
> > arm_smmu_v3-objs := $(arm_smmu_v3-objs-y)
> >
> > obj-$(CONFIG_ARM_SMMU_V3_PKVM) += arm_smmu_v3_kvm.o
> > +ccflags-$(CONFIG_ARM_SMMU_V3_PKVM) += -Iarch/arm64/kvm/
> > arm_smmu_v3_kvm-objs-y += arm-smmu-v3-kvm.o
> > arm_smmu_v3_kvm-objs-y += arm-smmu-v3-common.o
> > arm_smmu_v3_kvm-objs := $(arm_smmu_v3_kvm-objs-y)
> > diff --git a/include/kvm/iommu.h b/include/kvm/iommu.h
> > index ab888da731bc..82827b99b1ed 100644
> > --- a/include/kvm/iommu.h
> > +++ b/include/kvm/iommu.h
> > @@ -5,6 +5,12 @@
> > #include <asm/kvm_host.h>
> > #include <kvm/power_domain.h>
> > #include <linux/io-pgtable.h>
> > +#ifdef __KVM_NVHE_HYPERVISOR__
> > +#include <nvhe/spinlock.h>
> > +#else
> > +#include "hyp_constants.h"
> > +#endif
> >
> > /*
> > * Parameters from the trusted host:
> > @@ -23,6 +29,11 @@ struct kvm_hyp_iommu {
> >
> > struct io_pgtable_params *pgtable;
> > bool power_is_off;
> > +#ifdef __KVM_NVHE_HYPERVISOR__
> > + hyp_spinlock_t iommu_lock;
> > +#else
> > + u8 unused[HYP_SPINLOCK_SIZE];
> > +#endif
> > };
> >
> > struct kvm_hyp_iommu_memcache {
> > diff --git a/arch/arm64/kvm/hyp/nvhe/iommu/iommu.c b/arch/arm64/kvm/hyp/nvhe/iommu/iommu.c
> > index 1f4d5fcc1386..afaf173e65ed 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/iommu/iommu.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/iommu/iommu.c
> > @@ -14,12 +14,6 @@
> >
> > struct kvm_hyp_iommu_memcache __ro_after_init *kvm_hyp_iommu_memcaches;
> >
> > -/*
> > - * Serialize access to domains and IOMMU driver internal structures (command
> > - * queue, device tables)
> > - */
> > -static hyp_spinlock_t iommu_lock;
> > -
> > #define domain_to_iopt(_iommu, _domain, _domain_id) \
> > (struct io_pgtable) { \
> > .ops = &(_iommu)->pgtable->ops, \
> > @@ -93,10 +87,10 @@ int kvm_iommu_alloc_domain(pkvm_handle_t iommu_id, pkvm_handle_t domain_id,
> > {
> > int ret = -EINVAL;
> > struct io_pgtable iopt;
> > - struct kvm_hyp_iommu *iommu;
> > + struct kvm_hyp_iommu *iommu = kvm_iommu_ops.get_iommu_by_id(iommu_id);
> > struct kvm_hyp_iommu_domain *domain;
> >
> > - hyp_spin_lock(&iommu_lock);
> > + hyp_spin_lock(&iommu->iommu_lock);
> > domain = handle_to_domain(iommu_id, domain_id, &iommu);
> > if (!domain)
> > goto out_unlock;
> > @@ -112,7 +106,7 @@ int kvm_iommu_alloc_domain(pkvm_handle_t iommu_id, pkvm_handle_t domain_id,
> > domain->refs = 1;
> > domain->pgd = iopt.pgd;
> > out_unlock:
> > - hyp_spin_unlock(&iommu_lock);
> > + hyp_spin_unlock(&iommu->iommu_lock);
> > return ret;
> > }
> >
> > @@ -120,10 +114,10 @@ int kvm_iommu_free_domain(pkvm_handle_t iommu_id, pkvm_handle_t domain_id)
> > {
> > int ret = -EINVAL;
> > struct io_pgtable iopt;
> > - struct kvm_hyp_iommu *iommu;
> > + struct kvm_hyp_iommu *iommu = kvm_iommu_ops.get_iommu_by_id(iommu_id);
> > struct kvm_hyp_iommu_domain *domain;
> >
> > - hyp_spin_lock(&iommu_lock);
> > + hyp_spin_lock(&iommu->iommu_lock);
> > domain = handle_to_domain(iommu_id, domain_id, &iommu);
> > if (!domain)
> > goto out_unlock;
> > @@ -137,7 +131,7 @@ int kvm_iommu_free_domain(pkvm_handle_t iommu_id, pkvm_handle_t domain_id)
> > memset(domain, 0, sizeof(*domain));
> >
> > out_unlock:
> > - hyp_spin_unlock(&iommu_lock);
> > + hyp_spin_unlock(&iommu->iommu_lock);
> > return ret;
> > }
> > --
> >
> > (I didn't include full patch as it is too long, but mainly the
> > rest is s/&iommu_lock/&iommu->iommu_lock)
> >
> > Please let me know what do you think?
>
> It makes sense, I can append it to my tree or squash it (with your S-o-B)
> if you want to send the full patch
Sure, that is the full patch based on latest
https://jpbrucker.net/git/linux/log/?h=pkvm/smmu

Thanks,
Mostafa

--

From 5b43b97ca2486d52aa2ad475e4a34357dea57bca Mon Sep 17 00:00:00 2001
From: Mostafa Saleh <smostafa@google.com>
Date: Tue, 13 Jun 2023 14:59:37 +0000
Subject: [PATCH] KVM: arm: iommu: Use per-iommu lock instead of one global
lock

Currently, there is one big lock for all of the IOMMU operations
which is used to protect per-IOMMU resources or domains (which are
currently per-IOMMU also).

This can be improved for setups with many IOMMUs by having a per
IOMMU lock.

As now we always get the iommu before calling handle_to_domain, we
can remove the out_iommu arg and iommu_id and pass iommu instead.

Signed-off-by: Mostafa Saleh <smostafa@google.com>
---
arch/arm64/kvm/hyp/hyp-constants.c | 1 +
arch/arm64/kvm/hyp/nvhe/iommu/iommu.c | 75 +++++++++++++-------------
drivers/iommu/arm/arm-smmu-v3/Makefile | 1 +
include/kvm/iommu.h | 10 ++++
4 files changed, 48 insertions(+), 39 deletions(-)

diff --git a/arch/arm64/kvm/hyp/hyp-constants.c b/arch/arm64/kvm/hyp/hyp-constants.c
index b257a3b4bfc5..d84cc8ec1e46 100644
--- a/arch/arm64/kvm/hyp/hyp-constants.c
+++ b/arch/arm64/kvm/hyp/hyp-constants.c
@@ -9,5 +9,6 @@ int main(void)
DEFINE(STRUCT_HYP_PAGE_SIZE, sizeof(struct hyp_page));
DEFINE(PKVM_HYP_VM_SIZE, sizeof(struct pkvm_hyp_vm));
DEFINE(PKVM_HYP_VCPU_SIZE, sizeof(struct pkvm_hyp_vcpu));
+ DEFINE(HYP_SPINLOCK_SIZE, sizeof(hyp_spinlock_t));
return 0;
}
diff --git a/arch/arm64/kvm/hyp/nvhe/iommu/iommu.c b/arch/arm64/kvm/hyp/nvhe/iommu/iommu.c
index c70d3b6934eb..1dcba39d1d41 100644
--- a/arch/arm64/kvm/hyp/nvhe/iommu/iommu.c
+++ b/arch/arm64/kvm/hyp/nvhe/iommu/iommu.c
@@ -14,12 +14,6 @@

struct kvm_hyp_iommu_memcache __ro_after_init *kvm_hyp_iommu_memcaches;

-/*
- * Serialize access to domains and IOMMU driver internal structures (command
- * queue, device tables)
- */
-static hyp_spinlock_t iommu_lock;
-
#define domain_to_iopt(_iommu, _domain, _domain_id) \
(struct io_pgtable) { \
.ops = &(_iommu)->pgtable->ops, \
@@ -59,14 +53,11 @@ void kvm_iommu_reclaim_page(void *p)
}

static struct kvm_hyp_iommu_domain *
-handle_to_domain(pkvm_handle_t iommu_id, pkvm_handle_t domain_id,
- struct kvm_hyp_iommu **out_iommu)
+handle_to_domain(struct kvm_hyp_iommu *iommu, pkvm_handle_t domain_id)
{
int idx;
- struct kvm_hyp_iommu *iommu;
struct kvm_hyp_iommu_domain *domains;

- iommu = kvm_iommu_ops.get_iommu_by_id(iommu_id);
if (!iommu)
return NULL;

@@ -83,7 +74,6 @@ handle_to_domain(pkvm_handle_t iommu_id, pkvm_handle_t domain_id,
iommu->domains[idx] = domains;
}

- *out_iommu = iommu;
return &domains[domain_id & KVM_IOMMU_DOMAIN_ID_LEAF_MASK];
}

@@ -95,8 +85,9 @@ int kvm_iommu_alloc_domain(pkvm_handle_t iommu_id, pkvm_handle_t domain_id,
struct kvm_hyp_iommu *iommu;
struct kvm_hyp_iommu_domain *domain;

- hyp_spin_lock(&iommu_lock);
- domain = handle_to_domain(iommu_id, domain_id, &iommu);
+ iommu = kvm_iommu_ops.get_iommu_by_id(iommu_id);
+ hyp_spin_lock(&iommu->iommu_lock);
+ domain = handle_to_domain(iommu, domain_id);
if (!domain)
goto out_unlock;

@@ -111,7 +102,7 @@ int kvm_iommu_alloc_domain(pkvm_handle_t iommu_id, pkvm_handle_t domain_id,
domain->refs = 1;
domain->pgd = iopt.pgd;
out_unlock:
- hyp_spin_unlock(&iommu_lock);
+ hyp_spin_unlock(&iommu->iommu_lock);
return ret;
}

@@ -122,8 +113,9 @@ int kvm_iommu_free_domain(pkvm_handle_t iommu_id, pkvm_handle_t domain_id)
struct kvm_hyp_iommu *iommu;
struct kvm_hyp_iommu_domain *domain;

- hyp_spin_lock(&iommu_lock);
- domain = handle_to_domain(iommu_id, domain_id, &iommu);
+ iommu = kvm_iommu_ops.get_iommu_by_id(iommu_id);
+ hyp_spin_lock(&iommu->iommu_lock);
+ domain = handle_to_domain(iommu, domain_id);
if (!domain)
goto out_unlock;

@@ -136,7 +128,7 @@ int kvm_iommu_free_domain(pkvm_handle_t iommu_id, pkvm_handle_t domain_id)
memset(domain, 0, sizeof(*domain));

out_unlock:
- hyp_spin_unlock(&iommu_lock);
+ hyp_spin_unlock(&iommu->iommu_lock);
return ret;
}

@@ -147,8 +139,9 @@ int kvm_iommu_attach_dev(pkvm_handle_t iommu_id, pkvm_handle_t domain_id,
struct kvm_hyp_iommu *iommu;
struct kvm_hyp_iommu_domain *domain;

- hyp_spin_lock(&iommu_lock);
- domain = handle_to_domain(iommu_id, domain_id, &iommu);
+ iommu = kvm_iommu_ops.get_iommu_by_id(iommu_id);
+ hyp_spin_lock(&iommu->iommu_lock);
+ domain = handle_to_domain(iommu, domain_id);
if (!domain || !domain->refs || domain->refs == UINT_MAX)
goto out_unlock;

@@ -158,7 +151,7 @@ int kvm_iommu_attach_dev(pkvm_handle_t iommu_id, pkvm_handle_t domain_id,

domain->refs++;
out_unlock:
- hyp_spin_unlock(&iommu_lock);
+ hyp_spin_unlock(&iommu->iommu_lock);
return ret;
}

@@ -169,8 +162,9 @@ int kvm_iommu_detach_dev(pkvm_handle_t iommu_id, pkvm_handle_t domain_id,
struct kvm_hyp_iommu *iommu;
struct kvm_hyp_iommu_domain *domain;

- hyp_spin_lock(&iommu_lock);
- domain = handle_to_domain(iommu_id, domain_id, &iommu);
+ iommu = kvm_iommu_ops.get_iommu_by_id(iommu_id);
+ hyp_spin_lock(&iommu->iommu_lock);
+ domain = handle_to_domain(iommu, domain_id);
if (!domain || domain->refs <= 1)
goto out_unlock;

@@ -180,7 +174,7 @@ int kvm_iommu_detach_dev(pkvm_handle_t iommu_id, pkvm_handle_t domain_id,

domain->refs--;
out_unlock:
- hyp_spin_unlock(&iommu_lock);
+ hyp_spin_unlock(&iommu->iommu_lock);
return ret;
}

@@ -209,9 +203,10 @@ int kvm_iommu_map_pages(pkvm_handle_t iommu_id, pkvm_handle_t domain_id,
iova + size < iova || paddr + size < paddr)
return -EOVERFLOW;

- hyp_spin_lock(&iommu_lock);
+ iommu = kvm_iommu_ops.get_iommu_by_id(iommu_id);
+ hyp_spin_lock(&iommu->iommu_lock);

- domain = handle_to_domain(iommu_id, domain_id, &iommu);
+ domain = handle_to_domain(iommu, domain_id);
if (!domain)
goto err_unlock;

@@ -236,7 +231,7 @@ int kvm_iommu_map_pages(pkvm_handle_t iommu_id, pkvm_handle_t domain_id,
paddr += mapped;
}

- hyp_spin_unlock(&iommu_lock);
+ hyp_spin_unlock(&iommu->iommu_lock);
return 0;

err_unmap:
@@ -245,7 +240,7 @@ int kvm_iommu_map_pages(pkvm_handle_t iommu_id, pkvm_handle_t domain_id,
iopt_unmap_pages(&iopt, iova_orig, pgsize, pgcount, NULL);
__pkvm_host_unshare_dma(paddr_orig, size);
err_unlock:
- hyp_spin_unlock(&iommu_lock);
+ hyp_spin_unlock(&iommu->iommu_lock);
return ret;
}

@@ -269,8 +264,9 @@ size_t kvm_iommu_unmap_pages(pkvm_handle_t iommu_id, pkvm_handle_t domain_id,
iova + size < iova)
return 0;

- hyp_spin_lock(&iommu_lock);
- domain = handle_to_domain(iommu_id, domain_id, &iommu);
+ iommu = kvm_iommu_ops.get_iommu_by_id(iommu_id);
+ hyp_spin_lock(&iommu->iommu_lock);
+ domain = handle_to_domain(iommu, domain_id);
if (!domain)
goto out_unlock;

@@ -299,7 +295,7 @@ size_t kvm_iommu_unmap_pages(pkvm_handle_t iommu_id, pkvm_handle_t domain_id,
}

out_unlock:
- hyp_spin_unlock(&iommu_lock);
+ hyp_spin_unlock(&iommu->iommu_lock);
return total_unmapped;
}

@@ -311,14 +307,15 @@ phys_addr_t kvm_iommu_iova_to_phys(pkvm_handle_t iommu_id,
struct kvm_hyp_iommu *iommu;
struct kvm_hyp_iommu_domain *domain;

- hyp_spin_lock(&iommu_lock);
- domain = handle_to_domain(iommu_id, domain_id, &iommu);
+ iommu = kvm_iommu_ops.get_iommu_by_id(iommu_id);
+ hyp_spin_lock(&iommu->iommu_lock);
+ domain = handle_to_domain(iommu, domain_id);
if (domain) {
iopt = domain_to_iopt(iommu, domain, domain_id);

phys = iopt_iova_to_phys(&iopt, iova);
}
- hyp_spin_unlock(&iommu_lock);
+ hyp_spin_unlock(&iommu->iommu_lock);
return phys;
}

@@ -333,9 +330,9 @@ static int iommu_power_on(struct kvm_power_domain *pd)
* We currently assume that the device retains its architectural state
* across power off, hence no save/restore.
*/
- hyp_spin_lock(&iommu_lock);
+ hyp_spin_lock(&iommu->iommu_lock);
iommu->power_is_off = false;
- hyp_spin_unlock(&iommu_lock);
+ hyp_spin_unlock(&iommu->iommu_lock);
return 0;
}

@@ -346,9 +343,9 @@ static int iommu_power_off(struct kvm_power_domain *pd)

pkvm_debug("%s\n", __func__);

- hyp_spin_lock(&iommu_lock);
+ hyp_spin_lock(&iommu->iommu_lock);
iommu->power_is_off = true;
- hyp_spin_unlock(&iommu_lock);
+ hyp_spin_unlock(&iommu->iommu_lock);
return 0;
}

@@ -362,6 +359,8 @@ int kvm_iommu_init_device(struct kvm_hyp_iommu *iommu)
int ret;
void *domains;

+ hyp_spin_lock_init(&iommu->iommu_lock);
+
ret = pkvm_init_power_domain(&iommu->power_domain, &iommu_power_ops);
if (ret)
return ret;
@@ -376,8 +375,6 @@ int kvm_iommu_init(void)
{
enum kvm_pgtable_prot prot;

- hyp_spin_lock_init(&iommu_lock);
-
if (WARN_ON(!kvm_iommu_ops.get_iommu_by_id ||
!kvm_iommu_ops.alloc_iopt ||
!kvm_iommu_ops.free_iopt ||
diff --git a/drivers/iommu/arm/arm-smmu-v3/Makefile b/drivers/iommu/arm/arm-smmu-v3/Makefile
index a90b97d8bae3..cf9195e24a08 100644
--- a/drivers/iommu/arm/arm-smmu-v3/Makefile
+++ b/drivers/iommu/arm/arm-smmu-v3/Makefile
@@ -6,6 +6,7 @@ arm_smmu_v3-objs-$(CONFIG_ARM_SMMU_V3_SVA) += arm-smmu-v3-sva.o
arm_smmu_v3-objs := $(arm_smmu_v3-objs-y)

obj-$(CONFIG_ARM_SMMU_V3_PKVM) += arm_smmu_v3_kvm.o
+ccflags-$(CONFIG_ARM_SMMU_V3_PKVM) += -Iarch/arm64/kvm/
arm_smmu_v3_kvm-objs-y += arm-smmu-v3-kvm.o
arm_smmu_v3_kvm-objs-y += arm-smmu-v3-common.o
arm_smmu_v3_kvm-objs := $(arm_smmu_v3_kvm-objs-y)
diff --git a/include/kvm/iommu.h b/include/kvm/iommu.h
index ab888da731bc..b7cda7540156 100644
--- a/include/kvm/iommu.h
+++ b/include/kvm/iommu.h
@@ -5,6 +5,11 @@
#include <asm/kvm_host.h>
#include <kvm/power_domain.h>
#include <linux/io-pgtable.h>
+#ifdef __KVM_NVHE_HYPERVISOR__
+#include <nvhe/spinlock.h>
+#else
+#include "hyp_constants.h"
+#endif

/*
* Parameters from the trusted host:
@@ -23,6 +28,11 @@ struct kvm_hyp_iommu {

struct io_pgtable_params *pgtable;
bool power_is_off;
+#ifdef __KVM_NVHE_HYPERVISOR__
+ hyp_spinlock_t iommu_lock;
+#else
+ u8 unused[HYP_SPINLOCK_SIZE];
+#endif
};

struct kvm_hyp_iommu_memcache {
--
2.41.0.162.gfafddb0af9-goog