From: Julien Grall <julien.grall@arm.com>
To: Stefano Stabellini <sstabellini@kernel.org>
Cc: wei.chen@linaro.org, shankerd@codeaurora.org, xen-devel@lists.xen.org
Subject: Re: [PATCH] xen/arm: io: Protect the handlers with a read-write lock
Date: Mon, 11 Jul 2016 19:07:57 +0100 [thread overview]
Message-ID: <5783E07D.1030004@arm.com> (raw)
In-Reply-To: <alpine.DEB.2.10.1607111844460.26575@sstabellini-ThinkPad-X260>
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@arm.com>
>
> 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@kernel.org>
>
> 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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prev parent reply other threads:[~2016-07-11 18:07 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-28 16:34 [PATCH] xen/arm: io: Protect the handlers with a read-write lock Julien Grall
2016-07-11 17:49 ` Stefano Stabellini
2016-07-11 18:07 ` Julien Grall [this message]
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