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Message-ID:
<SN6PR02MB4157FE1A347214085549E72CD404A@SN6PR02MB4157.namprd02.prod.outlook.com>
Date: Sun, 31 Aug 2025 15:12:57 +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-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
CC: "kys@...rosoft.com" <kys@...rosoft.com>, "haiyangz@...rosoft.com"
<haiyangz@...rosoft.com>, "wei.liu@...nel.org" <wei.liu@...nel.org>,
"decui@...rosoft.com" <decui@...rosoft.com>, "arnd@...db.de" <arnd@...db.de>
Subject: RE: [PATCH] mshv: Add support for a new parent partition
configuration
From: Nuno Das Neves <nunodasneves@...ux.microsoft.com> Sent: Tuesday, August 19, 2025 12:29 AM
>
> Detect booting as an "L1VH" partition. This is a new scenario very
> similar to root partition where the mshv_root driver can be used to
> create and manage guest partitions.
>
> It mostly works the same as root partition, but there are some
> differences in how various features are handled. hv_l1vh_partition()
> is introduced to handle these cases. Add hv_parent_partition()
> which returns true for either case, replacing some hv_root_partition()
> checks.
>
> Signed-off-by: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
> ---
> drivers/hv/hv_common.c | 20 ++++++++++++--------
> drivers/hv/mshv_root_main.c | 22 ++++++++++++++--------
> include/asm-generic/mshyperv.h | 11 +++++++++++
> 3 files changed, 37 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
> index cbe4a954ad46..a6839593ca31 100644
> --- a/drivers/hv/hv_common.c
> +++ b/drivers/hv/hv_common.c
> @@ -357,7 +357,7 @@ int __init hv_common_init(void)
> hyperv_pcpu_arg = alloc_percpu(void *);
> BUG_ON(!hyperv_pcpu_arg);
>
> - if (hv_root_partition()) {
> + if (hv_parent_partition()) {
> hv_synic_eventring_tail = alloc_percpu(u8 *);
> BUG_ON(!hv_synic_eventring_tail);
> }
> @@ -506,7 +506,7 @@ int hv_common_cpu_init(unsigned int cpu)
> if (msr_vp_index > hv_max_vp_index)
> hv_max_vp_index = msr_vp_index;
>
> - if (hv_root_partition()) {
> + if (hv_parent_partition()) {
> synic_eventring_tail = (u8 **)this_cpu_ptr(hv_synic_eventring_tail);
> *synic_eventring_tail = kcalloc(HV_SYNIC_SINT_COUNT,
> sizeof(u8), flags);
> @@ -532,7 +532,7 @@ int hv_common_cpu_die(unsigned int cpu)
> * originally allocated memory is reused in hv_common_cpu_init().
> */
>
> - if (hv_root_partition()) {
> + if (hv_parent_partition()) {
> synic_eventring_tail = this_cpu_ptr(hv_synic_eventring_tail);
> kfree(*synic_eventring_tail);
> *synic_eventring_tail = NULL;
> @@ -703,13 +703,17 @@ void hv_identify_partition_type(void)
> * the root partition setting if also a Confidential VM.
> */
> if ((ms_hyperv.priv_high & HV_CREATE_PARTITIONS) &&
> - (ms_hyperv.priv_high & HV_CPU_MANAGEMENT) &&
> !(ms_hyperv.priv_high & HV_ISOLATION)) {
> - pr_info("Hyper-V: running as root partition\n");
> - if (IS_ENABLED(CONFIG_MSHV_ROOT))
> - hv_curr_partition_type = HV_PARTITION_TYPE_ROOT;
> - else
> +
> + if (!IS_ENABLED(CONFIG_MSHV_ROOT)) {
> pr_crit("Hyper-V: CONFIG_MSHV_ROOT not enabled!\n");
> + } else if (ms_hyperv.priv_high & HV_CPU_MANAGEMENT) {
> + pr_info("Hyper-V: running as root partition\n");
> + hv_curr_partition_type = HV_PARTITION_TYPE_ROOT;
> + } else {
> + pr_info("Hyper-V: running as L1VH partition\n");
> + hv_curr_partition_type = HV_PARTITION_TYPE_L1VH;
> + }
> }
> }
>
> diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
> index aca3331ad516..7c710703cd96 100644
> --- a/drivers/hv/mshv_root_main.c
> +++ b/drivers/hv/mshv_root_main.c
> @@ -37,12 +37,6 @@ MODULE_AUTHOR("Microsoft");
> MODULE_LICENSE("GPL");
> MODULE_DESCRIPTION("Microsoft Hyper-V root partition VMM interface /dev/mshv");
>
> -/* TODO move this to mshyperv.h when needed outside driver */
> -static inline bool hv_parent_partition(void)
> -{
> - return hv_root_partition();
> -}
> -
> /* TODO move this to another file when debugfs code is added */
> enum hv_stats_vp_counters { /* HV_THREAD_COUNTER */
> #if defined(CONFIG_X86)
> @@ -2190,6 +2184,15 @@ struct notifier_block mshv_reboot_nb = {
> .notifier_call = mshv_reboot_notify,
> };
>
> +static int __init mshv_l1vh_partition_init(struct device *dev)
> +{
> + hv_scheduler_type = HV_SCHEDULER_TYPE_CORE_SMT;
> + dev_info(dev, "Hypervisor using %s\n",
> + scheduler_type_to_string(hv_scheduler_type));
> +
> + return 0;
> +}
I'm a bit late reviewing this patch, but I have a suggestion. With this
function added, setting hv_scheduler_type and outputting the message
is now in two places: here and in mshv_retrieve_scheduler_type().
Instead, check for root vs. L1VH in mshv_retrieve_scheduler_type(),
and either call hv_retrieve_scheduler_type(), or force to
HV_SCHEDULER_TYPE_CORE_SMT. Then the rest of the code in
mshv_retrieve_scheduler_type(), including outputting the message,
just works. That puts all the logic about the scheduler type in one
place.
Then move the call to mshv_retrieve_scheduler_type() directly
into mshv_parent_partition_init() just before
if (hv_root_partition())
ret = mshv_root_partition_init(dev);
mshv_l1vh_partition_init() is no longer needed.
Independent of the suggestion, everything else looks good.
Reviewed-by: Michael Kelley <mhklinux@...look.com>
> +
> static void mshv_root_partition_exit(void)
> {
> unregister_reboot_notifier(&mshv_reboot_nb);
> @@ -2224,7 +2227,7 @@ static int __init mshv_parent_partition_init(void)
> struct device *dev;
> union hv_hypervisor_version_info version_info;
>
> - if (!hv_root_partition() || is_kdump_kernel())
> + if (!hv_parent_partition() || is_kdump_kernel())
> return -ENODEV;
>
> if (hv_get_hypervisor_version(&version_info))
> @@ -2261,7 +2264,10 @@ static int __init mshv_parent_partition_init(void)
>
> mshv_cpuhp_online = ret;
>
> - ret = mshv_root_partition_init(dev);
> + if (hv_root_partition())
> + ret = mshv_root_partition_init(dev);
> + else
> + ret = mshv_l1vh_partition_init(dev);
> if (ret)
> goto remove_cpu_state;
>
> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
> index dbbacd47ca35..f0f0eacb2eef 100644
> --- a/include/asm-generic/mshyperv.h
> +++ b/include/asm-generic/mshyperv.h
> @@ -31,6 +31,7 @@
> enum hv_partition_type {
> HV_PARTITION_TYPE_GUEST,
> HV_PARTITION_TYPE_ROOT,
> + HV_PARTITION_TYPE_L1VH,
> };
>
> struct ms_hyperv_info {
> @@ -457,12 +458,22 @@ static inline bool hv_root_partition(void)
> {
> return hv_curr_partition_type == HV_PARTITION_TYPE_ROOT;
> }
> +static inline bool hv_l1vh_partition(void)
> +{
> + return hv_curr_partition_type == HV_PARTITION_TYPE_L1VH;
> +}
> +static inline bool hv_parent_partition(void)
> +{
> + return hv_root_partition() || hv_l1vh_partition();
> +}
> 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 bool hv_l1vh_partition(void) { return false; }
> +static inline bool hv_parent_partition(void) { return false; }
> static inline int hv_call_deposit_pages(int node, u64 partition_id, u32 num_pages)
> {
> return -EOPNOTSUPP;
> --
> 2.34.1
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