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Message-ID:
<SN6PR02MB4157E39FBEFB18EB9A695EECD4332@SN6PR02MB4157.namprd02.prod.outlook.com>
Date: Sun, 8 Dec 2024 03:01:37 +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"
<linux-arm-kernel@...ts.infradead.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>, "catalin.marinas@....com"
<catalin.marinas@....com>, "will@...nel.org" <will@...nel.org>,
"tglx@...utronix.de" <tglx@...utronix.de>, "mingo@...hat.com"
<mingo@...hat.com>, "bp@...en8.de" <bp@...en8.de>,
"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>, "x86@...nel.org"
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<muminulrussell@...il.com>, "skinsburskii@...ux.microsoft.com"
<skinsburskii@...ux.microsoft.com>, "mukeshrathor@...rosoft.com"
<mukeshrathor@...rosoft.com>
Subject: RE: [PATCH 1/2] hyperv: Move hv_current_partition_id to arch-generic
code
From: Nuno Das Neves <nunodasneves@...ux.microsoft.com> Sent: Friday, December 6, 2024 2:22 PM
>
> Make hv_current_partition_id available in both x86_64 and arm64.
> This feature isn't specific to x86_64 and will be needed by common
> code.
>
> While at it, replace the BUG()s with WARN()s. Failing to get the id
> need not crash the machine (although it is a very bad sign).
>
> Signed-off-by: Nuno Das Neves <nudasnev@...rosoft.com>
> ---
> arch/arm64/hyperv/mshyperv.c | 3 +++
> arch/x86/hyperv/hv_init.c | 25 +------------------------
> arch/x86/include/asm/mshyperv.h | 2 --
> drivers/hv/hv_common.c | 23 +++++++++++++++++++++++
> include/asm-generic/mshyperv.h | 2 ++
> 5 files changed, 29 insertions(+), 26 deletions(-)
>
> diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
> index b1a4de4eee29..5050e748d266 100644
> --- a/arch/arm64/hyperv/mshyperv.c
> +++ b/arch/arm64/hyperv/mshyperv.c
> @@ -19,6 +19,9 @@
>
> static bool hyperv_initialized;
>
> +u64 hv_current_partition_id = HV_PARTITION_ID_SELF;
> +EXPORT_SYMBOL_GPL(hv_current_partition_id);
> +
Instead of adding a definition of hv_current_partition_id on
the arm64 side, couldn't the definition on the x86 side in
hv_init.c be moved to hv_common.c (or maybe somewhere
else that is specific to running in the root partition, per my
comments in the cover letter), so there is only one definition
shared by both architectures?
> int hv_get_hypervisor_version(union hv_hypervisor_version_info *info)
> {
> hv_get_vpreg_128(HV_REGISTER_HYPERVISOR_VERSION,
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index 95eada2994e1..950f5ccdb9d9 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -35,7 +35,7 @@
> #include <clocksource/hyperv_timer.h>
> #include <linux/highmem.h>
>
> -u64 hv_current_partition_id = ~0ull;
> +u64 hv_current_partition_id = HV_PARTITION_ID_SELF;
> EXPORT_SYMBOL_GPL(hv_current_partition_id);
>
> void *hv_hypercall_pg;
> @@ -394,24 +394,6 @@ static void __init hv_stimer_setup_percpu_clockev(void)
> old_setup_percpu_clockev();
> }
>
> -static void __init hv_get_partition_id(void)
> -{
> - struct hv_get_partition_id *output_page;
> - u64 status;
> - unsigned long flags;
> -
> - local_irq_save(flags);
> - output_page = *this_cpu_ptr(hyperv_pcpu_output_arg);
> - status = hv_do_hypercall(HVCALL_GET_PARTITION_ID, NULL, output_page);
> - if (!hv_result_success(status)) {
> - /* No point in proceeding if this failed */
> - pr_err("Failed to get partition ID: %lld\n", status);
> - BUG();
> - }
> - hv_current_partition_id = output_page->partition_id;
> - local_irq_restore(flags);
> -}
> -
> #if IS_ENABLED(CONFIG_HYPERV_VTL_MODE)
> static u8 __init get_vtl(void)
> {
> @@ -606,11 +588,6 @@ void __init hyperv_init(void)
>
> register_syscore_ops(&hv_syscore_ops);
>
> - if (cpuid_ebx(HYPERV_CPUID_FEATURES) & HV_ACCESS_PARTITION_ID)
> - hv_get_partition_id();
> -
> - BUG_ON(hv_root_partition && hv_current_partition_id == ~0ull);
> -
> #ifdef CONFIG_PCI_MSI
> /*
> * If we're running as root, we want to create our own PCI MSI domain.
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index 5f0bc6a6d025..9eeca2a6d047 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -44,8 +44,6 @@ extern bool hyperv_paravisor_present;
>
> extern void *hv_hypercall_pg;
>
> -extern u64 hv_current_partition_id;
> -
> extern union hv_ghcb * __percpu *hv_ghcb_pg;
>
> bool hv_isolation_type_snp(void);
> diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
> index 7a35c82976e0..819bcfd2b149 100644
> --- a/drivers/hv/hv_common.c
> +++ b/drivers/hv/hv_common.c
> @@ -278,11 +278,34 @@ static void hv_kmsg_dump_register(void)
> }
> }
>
> +static void __init hv_get_partition_id(void)
> +{
> + struct hv_get_partition_id *output_page;
> + u64 status;
> + unsigned long flags;
> +
> + local_irq_save(flags);
> + output_page = *this_cpu_ptr(hyperv_pcpu_output_arg);
> + status = hv_do_hypercall(HVCALL_GET_PARTITION_ID, NULL, output_page);
> + if (!hv_result_success(status)) {
> + local_irq_restore(flags);
> + WARN(true, "Failed to get partition ID: %lld\n", status);
> + return;
> + }
> + hv_current_partition_id = output_page->partition_id;
> + local_irq_restore(flags);
> +}
> +
> int __init hv_common_init(void)
> {
> int i;
> union hv_hypervisor_version_info version;
>
> + if (ms_hyperv.priv_high & HV_ACCESS_PARTITION_ID)
> + hv_get_partition_id();
hv_get_partition_id() uses the hyperv_pcpu_output_arg, and at
this point, hyperv_pcpu_output_arg isn't set. That setup
is done later in hv_common_init().
> +
> + WARN_ON(hv_root_partition && hv_current_partition_id == HV_PARTITION_ID_SELF);
> +
Since the hypercall will fail cleanly if the calling VM doesn't
have the HV_ACCESS_PARTITION_ID privilege, could the
above be simplified to just this?
if (hv_root_partition)
hv_get_partition_id():
A non-root partition VM doesn't need to get the partition ID, while a
root partition should have the privilege. If the hypercall fails, there's
already a WARN, so there's no value in doing another WARN. Also if
the hypercall succeeds, it presumably returns a specific partitionID, not
HV_PARTITION_ID_SELF, so we know we have what we want.
There's already an "if (hv_root_partition)" statement for setting up
the hyperv_pcpu_output_arg. The call to hv_get_partition_id() could
go under that existing "if" *after* the hyperv_pcpu_output_arg is
set. :-)
Michael
> /* Get information about the Hyper-V host version */
> if (!hv_get_hypervisor_version(&version))
> pr_info("Hyper-V: Host Build %d.%d.%d.%d-%d-%d\n",
> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
> index 8fe7aaab2599..8c4ff6e9aae7 100644
> --- a/include/asm-generic/mshyperv.h
> +++ b/include/asm-generic/mshyperv.h
> @@ -60,6 +60,8 @@ struct ms_hyperv_info {
> extern struct ms_hyperv_info ms_hyperv;
> extern bool hv_nested;
>
> +extern u64 hv_current_partition_id;
> +
> extern void * __percpu *hyperv_pcpu_input_arg;
> extern void * __percpu *hyperv_pcpu_output_arg;
>
> --
> 2.34.1
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