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

Oleksandr
2022-04-27T07:48:53Z

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