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SubjectRe: [PATCH] xen: don't require virtio with grants for non-PV guests
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On 15.06.22 11:25, Viresh Kumar wrote:
> On 15-06-22, 10:48, Juergen Gross wrote:
>> Commit fa1f57421e0b ("xen/virtio: Enable restricted memory access using
>> Xen grant mappings") introduced a new requirement for using virtio
>> devices: the backend now needs to support the VIRTIO_F_ACCESS_PLATFORM
>> feature.
>>
>> This is an undue requirement for non-PV guests, as those can be operated
>> with existing backends without any problem, as long as those backends
>> are running in dom0.
>>
>> Per default allow virtio devices without grant support for non-PV
>> guests.
>>
>> The setting can be overridden by using the new "xen_virtio_grant"
>> command line parameter.
>>
>> Add a new config item to always force use of grants for virtio.
>>
>> Fixes: fa1f57421e0b ("xen/virtio: Enable restricted memory access using Xen grant mappings")
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>> ---
>> .../admin-guide/kernel-parameters.txt | 6 +++++
>> drivers/xen/Kconfig | 9 ++++++++
>> drivers/xen/grant-dma-ops.c | 22 +++++++++++++++++++
>> include/xen/xen.h | 12 +++++-----
>> 4 files changed, 42 insertions(+), 7 deletions(-)
>
> Thanks for the quick fix.
>
> With CONFIG_DEBUG_SECTION_MISMATCH=y, this generates a warning.
>
> WARNING: modpost: vmlinux.o(.text+0x7a8270): Section mismatch in reference from the function xen_set_restricted_virtio_memory_access() to the variable .init.data:xen_virtio_grants
> The function xen_set_restricted_virtio_memory_access() references
> the variable __initdata xen_virtio_grants.
> This is often because xen_set_restricted_virtio_memory_access lacks a __initdata
> annotation or the annotation of xen_virtio_grants is wrong.

Silly me. Thanks for the notice.

>
> This can be fixed by:
>
> diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
> index d1fae789dfad..1099097b4515 100644
> --- a/drivers/xen/grant-dma-ops.c
> +++ b/drivers/xen/grant-dma-ops.c
> @@ -42,7 +42,7 @@ static __init int parse_use_grants(char *arg)
> }
> early_param("xen_virtio_grant", parse_use_grants);
>
> -void xen_set_restricted_virtio_memory_access(void)
> +void __init xen_set_restricted_virtio_memory_access(void)
> {
> if (IS_ENABLED(CONFIG_XEN_VIRTIO_FORCE_GRANT) || xen_virtio_grants ||
> (!xen_virtio_grants_set && xen_pv_domain()))
>
> With that:
>
> Tested-by: Viresh Kumar <viresh.kumar@linaro.org>
>

Thanks,


Juergen
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