Re: [PATCH 0/2] kernel: add new infrastructure for platform_has() support

[Oleksandr <olekstysh@gmail.com>]

On 26.04.22 16:40, Juergen Gross wrote:

Hello Juergen, all

> In another patch series [1] the need has come up to have support for
> a generic feature flag infrastructure.
>
> This patch series is introducing that infrastructure and adds the first
> use case.
>
> I have decided to use a similar interface as the already known x86
> cpu_has() function. As the new infrastructure is meant to be usable for
> general and arch-specific feature flags, the flags are being spread
> between a general bitmap and an arch specific one.
>
> The bitmaps start all being zero, single features can be set or reset
> at any time by using the related platform_[re]set_feature() functions.
>
> The platform_has() function is using a simple test_bit() call for now,
> further optimization might be added when needed.
>
> [1]: https://lore.kernel.org/lkml/1650646263-22047-1-git-send-email-olekstysh@gmail.com/T/#t

I have tested the series on Arm64 in the context of xen-virtio enabling 
work. I didn't see any issues with it. Thank you.

I reworked patch #3 [1] to use new functionality:


diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index ec5b082..f3b9e20 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -438,6 +438,8 @@ static int __init xen_guest_init(void)
         if (!xen_domain())
                 return 0;

+       xen_set_restricted_virtio_memory_access();
+
         if (!acpi_disabled)
                 xen_acpi_guest_init();
         else
diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
index 517a9d8..8b71b1d 100644
--- a/arch/x86/xen/enlighten_hvm.c
+++ b/arch/x86/xen/enlighten_hvm.c
@@ -195,6 +195,8 @@ static void __init xen_hvm_guest_init(void)
         if (xen_pv_domain())
                 return;

+       xen_set_restricted_virtio_memory_access();
+
         init_hvm_pv_info();

         reserve_shared_info();
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 5038edb..fcd5d5d 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -109,6 +109,8 @@ static DEFINE_PER_CPU(struct tls_descs, 
shadow_tls_desc);

  static void __init xen_pv_init_platform(void)
  {
+       xen_set_restricted_virtio_memory_access();
+
         populate_extra_pte(fix_to_virt(FIX_PARAVIRT_BOOTMAP));

         set_fixmap(FIX_PARAVIRT_BOOTMAP, xen_start_info->shared_info);
diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index 313a9127..a7bd8ce 100644
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -339,4 +339,15 @@ config XEN_GRANT_DMA_OPS
         bool
         select DMA_OPS

+config XEN_VIRTIO
+       bool "Xen virtio support"
+       depends on VIRTIO
+       select XEN_GRANT_DMA_OPS
+       help
+         Enable virtio support for running as Xen guest. Depending on the
+         guest type this will require special support on the backend side
+         (qemu or kernel, depending on the virtio device types used).
+
+         If in doubt, say n.
+
  endmenu
diff --git a/include/xen/xen.h b/include/xen/xen.h
index a99bab8..e2849c9 100644
--- a/include/xen/xen.h
+++ b/include/xen/xen.h
@@ -52,6 +52,14 @@ bool xen_biovec_phys_mergeable(const struct bio_vec 
*vec1,
  extern u64 xen_saved_max_mem_size;
  #endif

+#include <linux/platform-feature.h>
+
+static inline void xen_set_restricted_virtio_memory_access(void)
+{
+       if (IS_ENABLED(CONFIG_XEN_VIRTIO) && xen_domain())
+ platform_set_feature(PLATFORM_VIRTIO_RESTRICTED_MEM_ACCESS);
+}
+
  #ifdef CONFIG_XEN_UNPOPULATED_ALLOC
  int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page 
**pages);
  void xen_free_unpopulated_pages(unsigned int nr_pages, struct page 
**pages);
(END)


[1] 
https://lore.kernel.org/lkml/1650646263-22047-4-git-send-email-olekstysh@gmail.com/


>
> Juergen Gross (2):
>    kernel: add platform_has() infrastructure
>    virtio: replace arch_has_restricted_virtio_memory_access()
>
>   MAINTAINERS                            |  8 +++++++
>   arch/s390/Kconfig                      |  1 -
>   arch/s390/mm/init.c                    | 13 +++--------
>   arch/x86/Kconfig                       |  1 -
>   arch/x86/kernel/cpu/mshyperv.c         |  5 ++++-
>   arch/x86/mm/mem_encrypt.c              |  6 ------
>   arch/x86/mm/mem_encrypt_identity.c     |  5 +++++
>   drivers/virtio/Kconfig                 |  6 ------
>   drivers/virtio/virtio.c                |  5 ++---
>   include/asm-generic/Kbuild             |  1 +
>   include/asm-generic/platform-feature.h |  8 +++++++
>   include/linux/platform-feature.h       | 30 ++++++++++++++++++++++++++
>   include/linux/virtio_config.h          |  9 --------
>   kernel/Makefile                        |  2 +-
>   kernel/platform-feature.c              |  7 ++++++
>   15 files changed, 69 insertions(+), 38 deletions(-)
>   create mode 100644 include/asm-generic/platform-feature.h
>   create mode 100644 include/linux/platform-feature.h
>   create mode 100644 kernel/platform-feature.c
>
-- 
Regards,

Oleksandr Tyshchenko