Re: [RFC PATCH 4/6] virtio: Various updates to xen-virtio DMA ops layer

[Oleksandr <olekstysh@gmail.com>]

Hello Stefano, Juergen


On 19.04.22 09:58, Juergen Gross wrote:
> On 18.04.22 21:11, Stefano Stabellini wrote:
>> On Sun, 17 Apr 2022, Oleksandr wrote:
>>> On 16.04.22 01:02, Stefano Stabellini wrote:
>>>> On Thu, 14 Apr 2022, Oleksandr Tyshchenko wrote:
>>>>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>>>>
>>>>> In the context of current patch do the following:
>>>>> 1. Update code to support virtio-mmio devices
>>>>> 2. Introduce struct xen_virtio_data and account passed virtio devices
>>>>>      (using list) as we need to store some per-device data
>>>>> 3. Add multi-page support for xen_virtio_dma_map(unmap)_page 
>>>>> callbacks
>>>>> 4. Harden code against malicious backend
>>>>> 5. Change to use alloc_pages_exact() instead of __get_free_pages()
>>>>> 6. Introduce locking scheme to protect mappings (I am not 100% sure
>>>>>      whether per-device lock is really needed)
>>>>> 7. Handle virtio device's DMA mask
>>>>> 8. Retrieve the ID of backend domain from DT for virtio-mmio device
>>>>>      instead of hardcoding it.
>>>>>
>>>>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>>>> ---
>>>>>    arch/arm/xen/enlighten.c |  11 +++
>>>>>    drivers/xen/Kconfig      |   2 +-
>>>>>    drivers/xen/xen-virtio.c | 200
>>>>> ++++++++++++++++++++++++++++++++++++++++++-----
>>>>>    include/xen/xen-ops.h    |   5 ++
>>>>>    4 files changed, 196 insertions(+), 22 deletions(-)
>>>>>
>>>>> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
>>>>> index ec5b082..870d92f 100644
>>>>> --- a/arch/arm/xen/enlighten.c
>>>>> +++ b/arch/arm/xen/enlighten.c
>>>>> @@ -409,6 +409,17 @@ int __init arch_xen_unpopulated_init(struct 
>>>>> resource
>>>>> **res)
>>>>>    }
>>>>>    #endif
>>>>>    +#ifdef CONFIG_ARCH_HAS_RESTRICTED_VIRTIO_MEMORY_ACCESS
>>>>> +int arch_has_restricted_virtio_memory_access(void)
>>>>> +{
>>>>> +    if (IS_ENABLED(CONFIG_XEN_HVM_VIRTIO_GRANT) && xen_hvm_domain())
>>>>> +        return 1;
>>>> Instead of xen_hvm_domain(), you can just use xen_domain(). Also there
>>>> is no need for the #ifdef
>>>> CONFIG_ARCH_HAS_RESTRICTED_VIRTIO_MEMORY_ACCESS, given that:
>>>>
>>>> CONFIG_XEN_HVM_VIRTIO_GRANT depends on XEN_VIRTIO which selects
>>>> ARCH_HAS_RESTRICTED_VIRTIO_MEMORY_ACCESS
>>>
>>>
>>> Yes, but please see my comments in commit #2 regarding
>>> CONFIG_XEN_HVM_VIRTIO_GRANT option and
>>> arch_has_restricted_virtio_memory_access() on Arm.
>>>
>>> I propose to have the following on Arm:
>>>
>>> int arch_has_restricted_virtio_memory_access(void)
>>> {
>>>       return xen_has_restricted_virtio_memory_access();
>>> }
>>>
>>>
>>> where common xen.h contain a helper to be used by both Arm and x86:
>>>
>>> static inline int xen_has_restricted_virtio_memory_access(void)
>>> {
>>>       if (IS_ENABLED(CONFIG_XEN_VIRTIO) && (xen_pv_domain() ||
>>> xen_hvm_domain()))
>>>           return 1;
>>>
>>>       return 0;
>>> }
>>>
>>>
>>> But I would be happy with what you propose as well.
>>
>> As I wrote in the previous reply, I also prefer to share the code
>> between x86 and ARM, and I think it could look like:
>>
>> int arch_has_restricted_virtio_memory_access(void)
>> {
>>       return xen_has_restricted_virtio_memory_access();
>> }
>> [...]
>> static inline int xen_has_restricted_virtio_memory_access(void)
>> {
>>       return (IS_ENABLED(CONFIG_XEN_VIRTIO) && xen_domain());
>> }
>>
>> But let's check with Juergen and Boris.


for the record, it is already clarified in commit #2, I will use this 
variant.


>>
>>
>>
>>>>> +    return 0;
>>>>> +}
>>>>> +EXPORT_SYMBOL_GPL(arch_has_restricted_virtio_memory_access);
>>>>> +#endif
>>>>> +
>>>>>    static void __init xen_dt_guest_init(void)
>>>>>    {
>>>>>        struct device_node *xen_node;
>>>>> diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
>>>>> index fc61f7a..56afe6a 100644
>>>>> --- a/drivers/xen/Kconfig
>>>>> +++ b/drivers/xen/Kconfig
>>>>> @@ -347,7 +347,7 @@ config XEN_VIRTIO
>>>>>      config XEN_HVM_VIRTIO_GRANT
>>>>>        bool "Require virtio for fully virtualized guests to use grant
>>>>> mappings"
>>>>> -    depends on XEN_VIRTIO && X86_64
>>>>> +    depends on XEN_VIRTIO && (X86_64 || ARM || ARM64)
>>>> you can remove the architectural dependencies
>>>
>>>
>>> According to the conversation in commit #2 we are considering just a 
>>> single
>>> XEN_VIRTIO option, but it is going to has the
>>> same architectural dependencies: (X86_64 || ARM || ARM64)
>>>
>>> By removing the architectural dependencies here, we will leave also 
>>> X86_32
>>> covered (neither XEN_HVM_VIRTIO_GRANT nor XEN_PV_VIRTIO covered it). 
>>> I don't
>>> know whether it is ok or not.
>>>
>>> Shall I remove dependencies anyway?
>>
>> No, good point. I don't know about X86_32. This is another detail where
>> Juergen or Boris should comment.
>
> X86_32 should in theory work (it is HVM/PVH only, as PV 32-bit guests 
> are no
> longer supported).


ok, thank you for confirming. I will drop architectural dependencies then.


>
>
>
> Juergen

-- 
Regards,

Oleksandr Tyshchenko