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Re: [Xen-devel] [PATCH] xen/arm: io: Protect the handlers with a read-write lock
Hi Stefano,
On 11/07/16 18:49, Stefano Stabellini wrote:
On Tue, 28 Jun 2016, Julien Grall wrote:
Currently, accessing the I/O handlers does not require to take a lock
because new handlers are always added at the end of the array. In a
follow-up patch, this array will be sort to optimize the look up.
Given that most of the time the I/O handlers will not be modify,
using a spinlock will add contention when multiple vCPU are accessing
the emulated MMIOs. So use a read-write lock to protected the handlers.
Finally, take the opportunity to re-indent correctly domain_io_init.
Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
I would appreciate if you could avoid mixing indentation changes with
other changes in the future.
The indentation changes was very small and I did not feel it was
necessary to have a separate patch for it. I tend to limit the number of
patches unless it hides important changes.
Anyway, I will try to split coding style changes and functional changes
in the future.
Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
I'll commit.
Thank you!
Regards,
xen/arch/arm/io.c | 47 +++++++++++++++++++++++++++-------------------
xen/include/asm-arm/mmio.h | 3 ++-
2 files changed, 30 insertions(+), 20 deletions(-)
diff --git a/xen/arch/arm/io.c b/xen/arch/arm/io.c
index 0156755..5a96836 100644
--- a/xen/arch/arm/io.c
+++ b/xen/arch/arm/io.c
@@ -70,23 +70,39 @@ static int handle_write(const struct mmio_handler *handler,
struct vcpu *v,
handler->priv);
}
-int handle_mmio(mmio_info_t *info)
+static const struct mmio_handler *find_mmio_handler(struct domain *d,
+ paddr_t gpa)
{
- struct vcpu *v = current;
- int i;
- const struct mmio_handler *handler = NULL;
- const struct vmmio *vmmio = &v->domain->arch.vmmio;
+ const struct mmio_handler *handler;
+ unsigned int i;
+ struct vmmio *vmmio = &d->arch.vmmio;
+
+ read_lock(&vmmio->lock);
for ( i = 0; i < vmmio->num_entries; i++ )
{
handler = &vmmio->handlers[i];
- if ( (info->gpa >= handler->addr) &&
- (info->gpa < (handler->addr + handler->size)) )
+ if ( (gpa >= handler->addr) &&
+ (gpa < (handler->addr + handler->size)) )
break;
}
if ( i == vmmio->num_entries )
+ handler = NULL;
+
+ read_unlock(&vmmio->lock);
+
+ return handler;
+}
+
+int handle_mmio(mmio_info_t *info)
+{
+ struct vcpu *v = current;
+ const struct mmio_handler *handler = NULL;
+
+ handler = find_mmio_handler(v->domain, info->gpa);
+ if ( !handler )
return 0;
if ( info->dabt.write )
@@ -104,7 +120,7 @@ void register_mmio_handler(struct domain *d,
BUG_ON(vmmio->num_entries >= MAX_IO_HANDLER);
- spin_lock(&vmmio->lock);
+ write_lock(&vmmio->lock);
handler = &vmmio->handlers[vmmio->num_entries];
@@ -113,24 +129,17 @@ void register_mmio_handler(struct domain *d,
handler->size = size;
handler->priv = priv;
- /*
- * handle_mmio is not using the lock to avoid contention.
- * Make sure the other processors see the new handler before
- * updating the number of entries
- */
- dsb(ish);
-
vmmio->num_entries++;
- spin_unlock(&vmmio->lock);
+ write_unlock(&vmmio->lock);
}
int domain_io_init(struct domain *d)
{
- spin_lock_init(&d->arch.vmmio.lock);
- d->arch.vmmio.num_entries = 0;
+ rwlock_init(&d->arch.vmmio.lock);
+ d->arch.vmmio.num_entries = 0;
- return 0;
+ return 0;
}
/*
diff --git a/xen/include/asm-arm/mmio.h b/xen/include/asm-arm/mmio.h
index da1cc2e..32f10f2 100644
--- a/xen/include/asm-arm/mmio.h
+++ b/xen/include/asm-arm/mmio.h
@@ -20,6 +20,7 @@
#define __ASM_ARM_MMIO_H__
#include <xen/lib.h>
+#include <xen/rwlock.h>
#include <asm/processor.h>
#include <asm/regs.h>
@@ -51,7 +52,7 @@ struct mmio_handler {
struct vmmio {
int num_entries;
- spinlock_t lock;
+ rwlock_t lock;
struct mmio_handler handlers[MAX_IO_HANDLER];
};
--
1.9.1
--
Julien Grall
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