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Message-ID: <fec1aeb7-ea07-4363-9e6a-50b0c778e855@linux.microsoft.com>
Date: Tue, 10 Dec 2024 08:40:49 -0800
From: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
To: Michael Kelley <mhklinux@...look.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" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
"arnd@...db.de" <arnd@...db.de>,
"jinankjain@...ux.microsoft.com" <jinankjain@...ux.microsoft.com>,
"muminulrussell@...il.com" <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
On 12/7/2024 7:01 PM, Michael Kelley wrote:
> 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?
>
Yes, that's a better idea.
>> 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. :-)
>
Thank you, that makes sense. I'll make the changes you suggested for v2.
Nuno
> 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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