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

Juergen Gross
2022-04-19T06:59:03Z

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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.
>
>
>>>> + 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).

Juergen

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