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Message-ID:
<SN6PR02MB41570A2F04AF7C196D477BF6D4C72@SN6PR02MB4157.namprd02.prod.outlook.com>
Date: Fri, 21 Feb 2025 20:59:05 +0000
From: Michael Kelley <mhklinux@...look.com>
To: Nuno Das Neves <nunodasneves@...ux.microsoft.com>,
"linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org"
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<linux-arch@...r.kernel.org>, "iommu@...ts.linux.dev"
<iommu@...ts.linux.dev>, "eahariha@...ux.microsoft.com"
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<mukeshrathor@...rosoft.com>
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Subject: RE: [PATCH v3 3/3] hyperv: Add CONFIG_MSHV_ROOT to gate root
partition support
From: Nuno Das Neves <nunodasneves@...ux.microsoft.com> Sent: Friday, February 21, 2025 11:57 AM
>
> CONFIG_MSHV_ROOT allows kernels built to run as a normal Hyper-V guest
> to exclude the root partition code, which is expected to grow
> significantly over time.
>
> This option is a tristate so future driver code can be built as a
> (m)odule, allowing faster development iteration cycles.
>
> If CONFIG_MSHV_ROOT is disabled, don't compile hv_proc.c, and stub
> hv_root_partition() to return false unconditionally. This allows the
> compiler to optimize away root partition code blocks since they will
> be disabled at compile time.
>
> In the case of booting as root partition *without* CONFIG_MSHV_ROOT
> enabled, print a critical error (the kernel will likely crash).
>
> Signed-off-by: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
> Reviewed-by: Easwar Hariharan <eahariha@...ux.microsoft.com>
> ---
> drivers/hv/Kconfig | 16 ++++++++++++++++
> drivers/hv/Makefile | 3 ++-
> drivers/hv/hv_common.c | 5 ++++-
> include/asm-generic/mshyperv.h | 24 ++++++++++++++++++++----
> 4 files changed, 42 insertions(+), 6 deletions(-)
Reviewed-by: Michael Kelley <mhklinux@...look.com>
>
> diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
> index 862c47b191af..794e88e9dc6b 100644
> --- a/drivers/hv/Kconfig
> +++ b/drivers/hv/Kconfig
> @@ -55,4 +55,20 @@ config HYPERV_BALLOON
> help
> Select this option to enable Hyper-V Balloon driver.
>
> +config MSHV_ROOT
> + tristate "Microsoft Hyper-V root partition support"
> + depends on HYPERV
> + depends on !HYPERV_VTL_MODE
> + # The hypervisor interface operates on 4k pages. Enforcing it here
> + # simplifies many assumptions in the root partition code.
> + # e.g. When withdrawing memory, the hypervisor gives back 4k pages in
> + # no particular order, making it impossible to reassemble larger pages
> + depends on PAGE_SIZE_4KB
> + default n
> + help
> + Select this option to enable support for booting and running as root
> + partition on Microsoft Hyper-V.
> +
> + If unsure, say N.
> +
> endmenu
> diff --git a/drivers/hv/Makefile b/drivers/hv/Makefile
> index 9afcabb3fbd2..2b8dc954b350 100644
> --- a/drivers/hv/Makefile
> +++ b/drivers/hv/Makefile
> @@ -13,4 +13,5 @@ hv_vmbus-$(CONFIG_HYPERV_TESTING) += hv_debugfs.o
> hv_utils-y := hv_util.o hv_kvp.o hv_snapshot.o hv_utils_transport.o
>
> # Code that must be built-in
> -obj-$(subst m,y,$(CONFIG_HYPERV)) += hv_common.o hv_proc.o
> +obj-$(subst m,y,$(CONFIG_HYPERV)) += hv_common.o
> +obj-$(subst m,y,$(CONFIG_MSHV_ROOT)) += hv_proc.o
> diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
> index 3d9cfcfbc854..9804adb4cc56 100644
> --- a/drivers/hv/hv_common.c
> +++ b/drivers/hv/hv_common.c
> @@ -734,6 +734,9 @@ void hv_identify_partition_type(void)
> (ms_hyperv.priv_high & HV_CPU_MANAGEMENT) &&
> !(ms_hyperv.priv_high & HV_ISOLATION)) {
> pr_info("Hyper-V: running as root partition\n");
> - hv_curr_partition_type = HV_PARTITION_TYPE_ROOT;
> + if (IS_ENABLED(CONFIG_MSHV_ROOT))
> + hv_curr_partition_type = HV_PARTITION_TYPE_ROOT;
> + else
> + pr_crit("Hyper-V: CONFIG_MSHV_ROOT not enabled!\n");
> }
> }
> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
> index 54ebd630e72c..b13b0cda4ac8 100644
> --- a/include/asm-generic/mshyperv.h
> +++ b/include/asm-generic/mshyperv.h
> @@ -223,10 +223,6 @@ void *hv_alloc_hyperv_page(void);
> void *hv_alloc_hyperv_zeroed_page(void);
> void hv_free_hyperv_page(void *addr);
>
> -int hv_call_deposit_pages(int node, u64 partition_id, u32 num_pages);
> -int hv_call_add_logical_proc(int node, u32 lp_index, u32 acpi_id);
> -int hv_call_create_vp(int node, u64 partition_id, u32 vp_index, u32 flags);
> -
> /**
> * hv_cpu_number_to_vp_number() - Map CPU to VP.
> * @cpu_number: CPU number in Linux terms
> @@ -327,9 +323,29 @@ static inline enum hv_isolation_type
> hv_get_isolation_type(void)
> }
> #endif /* CONFIG_HYPERV */
>
> +#if IS_ENABLED(CONFIG_MSHV_ROOT)
> static inline bool hv_root_partition(void)
> {
> return hv_curr_partition_type == HV_PARTITION_TYPE_ROOT;
> }
> +int hv_call_deposit_pages(int node, u64 partition_id, u32 num_pages);
> +int hv_call_add_logical_proc(int node, u32 lp_index, u32 acpi_id);
> +int hv_call_create_vp(int node, u64 partition_id, u32 vp_index, u32 flags);
> +
> +#else /* CONFIG_MSHV_ROOT */
> +static inline bool hv_root_partition(void) { return false; }
> +static inline int hv_call_deposit_pages(int node, u64 partition_id, u32 num_pages)
> +{
> + return -EOPNOTSUPP;
> +}
> +static inline int hv_call_add_logical_proc(int node, u32 lp_index, u32 acpi_id)
> +{
> + return -EOPNOTSUPP;
> +}
> +static inline int hv_call_create_vp(int node, u64 partition_id, u32 vp_index, u32 flags)
> +{
> + return -EOPNOTSUPP;
> +}
> +#endif /* CONFIG_MSHV_ROOT */
>
> #endif
> --
> 2.34.1
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