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Message-ID: <573c2d9f-8df0-0e0f-2f57-e8ea85e403b4@gmail.com>
Date: Thu, 16 Jun 2022 10:31:42 +0300
From: Oleksandr <olekstysh@...il.com>
To: Juergen Gross <jgross@...e.com>
Cc: xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
viresh.kumar@...aro.org, hch@...radead.org,
Stefano Stabellini <sstabellini@...nel.org>,
Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
Subject: Re: [PATCH v2] xen: don't require virtio with grants for non-PV
guests
On 16.06.22 08:37, Juergen Gross wrote:
Hello Juergen
> 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.
>
> 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")
> Reported-by: Viresh Kumar <viresh.kumar@...aro.org>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
> V2:
> - remove command line parameter (Christoph Hellwig)
> ---
> drivers/xen/Kconfig | 9 +++++++++
> include/xen/xen.h | 2 +-
> 2 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
> index bfd5f4f706bc..a65bd92121a5 100644
> --- a/drivers/xen/Kconfig
> +++ b/drivers/xen/Kconfig
> @@ -355,4 +355,13 @@ config XEN_VIRTIO
>
> If in doubt, say n.
>
> +config XEN_VIRTIO_FORCE_GRANT
> + bool "Require Xen virtio support to use grants"
> + depends on XEN_VIRTIO
> + help
> + Require virtio for Xen guests to use grant mappings.
> + This will avoid the need to give the backend the right to map all
> + of the guest memory. This will need support on the backend side
> + (e.g. qemu or kernel, depending on the virtio device types used).
> +
> endmenu
> diff --git a/include/xen/xen.h b/include/xen/xen.h
> index 0780a81e140d..4d4188f20337 100644
> --- a/include/xen/xen.h
> +++ b/include/xen/xen.h
> @@ -56,7 +56,7 @@ extern u64 xen_saved_max_mem_size;
>
> static inline void xen_set_restricted_virtio_memory_access(void)
> {
> - if (IS_ENABLED(CONFIG_XEN_VIRTIO) && xen_domain())
> + if (IS_ENABLED(CONFIG_XEN_VIRTIO_FORCE_GRANT) || xen_pv_domain())
> platform_set(PLATFORM_VIRTIO_RESTRICTED_MEM_ACCESS);
Looks like, the flag will be *always* set for paravirtualized guests
even if CONFIG_XEN_VIRTIO disabled.
Maybe we should clarify the check?
if (IS_ENABLED(CONFIG_XEN_VIRTIO_FORCE_GRANT) ||
IS_ENABLED(CONFIG_XEN_VIRTIO) && xen_pv_domain())
platform_set(PLATFORM_VIRTIO_RESTRICTED_MEM_ACCESS);
> }
>
--
Regards,
Oleksandr Tyshchenko
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