linux-kernel - Re: [RFC PATCH 6/6] arm/xen: Assign xen-virtio DMA ops for virtio devices in Xen guests

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Message-ID: <8df1dc60-614a-67fa-3a9d-e2db4a7e0132@gmail.com>
Date:   Sun, 17 Apr 2022 22:20:04 +0300
From:   Oleksandr <olekstysh@...il.com>
To:     Stefano Stabellini <sstabellini@...nel.org>
Cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>, Julien Grall <julien@....org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [RFC PATCH 6/6] arm/xen: Assign xen-virtio DMA ops for virtio
 devices in Xen guests


On 16.04.22 01:02, Stefano Stabellini wrote:


Hello Stefano

> On Thu, 14 Apr 2022, Oleksandr Tyshchenko wrote:
>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
>>
>> Call xen_virtio_setup_dma_ops() only for Xen-aware virtio devices
>> in Xen guests if restricted access to the guest memory is enabled.
>>
>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
>> ---
>>   include/xen/arm/xen-ops.h | 7 +++++++
>>   1 file changed, 7 insertions(+)
>>
>> diff --git a/include/xen/arm/xen-ops.h b/include/xen/arm/xen-ops.h
>> index 621da05..28b2ad3 100644
>> --- a/include/xen/arm/xen-ops.h
>> +++ b/include/xen/arm/xen-ops.h
>> @@ -2,12 +2,19 @@
>>   #ifndef _ASM_ARM_XEN_OPS_H
>>   #define _ASM_ARM_XEN_OPS_H
>>   
>> +#include <linux/virtio_config.h>
>>   #include <xen/swiotlb-xen.h>
>> +#include <xen/xen-ops.h>
>>   
>>   static inline void xen_setup_dma_ops(struct device *dev)
>>   {
>>   	if (xen_swiotlb_detect())
>>   		dev->dma_ops = &xen_swiotlb_dma_ops;
>> +
>> +#ifdef CONFIG_XEN_VIRTIO
>> +	if (arch_has_restricted_virtio_memory_access() && xen_is_virtio_device(dev))
>> +		xen_virtio_setup_dma_ops(dev);
>> +#endif
> This makes sense overall.


thank you


> Considering that the swiotlb-xen case and the
> virtio case are mutually exclusive, I would write it like this:
>
> 	if (arch_has_restricted_virtio_memory_access() && xen_is_virtio_device(dev))
> 		xen_virtio_setup_dma_ops(dev);
> 	else if (xen_swiotlb_detect())
> 		dev->dma_ops = &xen_swiotlb_dma_ops;


Agree, will do


>
> There is no need for #ifdef (also see other comments).


Agree, if !CONFIG_XEN_VIRTIO then xen_virtio_ are just stubs.


#ifdef CONFIG_XEN_VIRTIO
void xen_virtio_setup_dma_ops(struct device *dev);
bool xen_is_virtio_device(struct device *dev);
#else
static inline void xen_virtio_setup_dma_ops(struct device *dev)
{
}
static inline bool xen_is_virtio_device(struct device *dev)
{
     return false;
}
#endif /* CONFIG_XEN_VIRTIO */



-- 
Regards,

Oleksandr Tyshchenko