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Message-ID:
<SN6PR02MB4157042605A22E40767DDC94D4EF2@SN6PR02MB4157.namprd02.prod.outlook.com>
Date: Tue, 28 Jan 2025 18:45:11 +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>, "wei.liu@...nel.org" <wei.liu@...nel.org>
CC: "kys@...rosoft.com" <kys@...rosoft.com>, "haiyangz@...rosoft.com"
<haiyangz@...rosoft.com>, "decui@...rosoft.com" <decui@...rosoft.com>,
"catalin.marinas@....com" <catalin.marinas@....com>, "will@...nel.org"
<will@...nel.org>, "tglx@...utronix.de" <tglx@...utronix.de>,
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"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>, "x86@...nel.org"
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<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 v2 1/2] hyperv: Move hv_current_partition_id to
arch-generic code
From: Nuno Das Neves <nunodasneves@...ux.microsoft.com> Sent: Wednesday, January 22, 2025 5:48 PM
>
> Move hv_current_partition_id and hv_get_partition_id() to hv_common.c.
> These aren't specific to x86_64 and will be needed by common code.
>
> Set hv_current_partition_id to HV_PARTITION_ID_SELF by default.
>
> Use a stack variable for the output of the hypercall. This allows moving
> the call of hv_get_partition_id() to hv_common_init() before the percpu
> pages are initialized.
>
> Remove the BUG()s. Failing to get the id need not crash the machine.
>
> Signed-off-by: Nuno Das Neves <nudasnev@...rosoft.com>
> ---
> arch/x86/hyperv/hv_init.c | 26 --------------------------
> arch/x86/include/asm/mshyperv.h | 2 --
> drivers/hv/hv_common.c | 23 +++++++++++++++++++++++
> include/asm-generic/mshyperv.h | 1 +
> 4 files changed, 24 insertions(+), 28 deletions(-)
>
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index 173005e6a95d..6b9f6f9f704d 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -34,9 +34,6 @@
> #include <clocksource/hyperv_timer.h>
> #include <linux/highmem.h>
>
> -u64 hv_current_partition_id = ~0ull;
> -EXPORT_SYMBOL_GPL(hv_current_partition_id);
> -
> void *hv_hypercall_pg;
> EXPORT_SYMBOL_GPL(hv_hypercall_pg);
>
> @@ -393,24 +390,6 @@ 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)
> {
> @@ -605,11 +584,6 @@ 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 f91ab1e75f9f..8d3ada3e8d0d 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -43,8 +43,6 @@ 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 af5d1dc451f6..1da19b64ef16 100644
> --- a/drivers/hv/hv_common.c
> +++ b/drivers/hv/hv_common.c
> @@ -31,6 +31,9 @@
> #include <hyperv/hvhdk.h>
> #include <asm/mshyperv.h>
>
> +u64 hv_current_partition_id = HV_PARTITION_ID_SELF;
> +EXPORT_SYMBOL_GPL(hv_current_partition_id);
> +
> /*
> * hv_root_partition, ms_hyperv and hv_nested are defined here with other
> * Hyper-V specific globals so they are shared across all architectures and are
> @@ -283,6 +286,23 @@ static inline bool hv_output_page_exists(void)
> return hv_root_partition || IS_ENABLED(CONFIG_HYPERV_VTL_MODE);
> }
>
> +static void __init hv_get_partition_id(void)
> +{
> + /*
> + * Note in this case the output can be on the stack because it is just
> + * a single u64 and hence won't cross a page boundary.
> + */
> + struct hv_get_partition_id output;
It's unfortunate that the structure name "hv_get_partition_id" is also
the name of this function. Could the structure name be changed to
follow the pattern of having "output" in the name, like other hypercall
parameters? It's not a blocker if it can't be changed. I was just surprised
to search for "hv_get_partition_id" and find both uses.
Also, see the comment at the beginning of hv_query_ext_cap() regarding
using a local stack variable as hypercall input or output. The comment
originated here [1]. At that time, I didn't investigate Sunil's assertion any
further, and I'm still unsure whether it is really true. But perhaps for
consistency and safety we should follow what it says.
[1] https://lore.kernel.org/linux-hyperv/SN4PR2101MB0880DB0606A5A0B72AD244B4C06A9@SN4PR2101MB0880.namprd21.prod.outlook.com/
> + u64 status;
> +
> + status = hv_do_hypercall(HVCALL_GET_PARTITION_ID, NULL, &output);
> + if (!hv_result_success(status)) {
> + pr_err("Hyper-V: failed to get partition ID: %#lx\n", status);
> + return;
> + }
> + hv_current_partition_id = output.partition_id;
> +}
> +
> int __init hv_common_init(void)
> {
> int i;
> @@ -298,6 +318,9 @@ int __init hv_common_init(void)
> if (hv_is_isolation_supported())
> sysctl_record_panic_msg = 0;
>
> + if (ms_hyperv.priv_high & HV_ACCESS_PARTITION_ID)
> + hv_get_partition_id();
I don't see how this works. On the x86 side, hv_common_init()
is called before the guest ID is set and the hypercall page is setup.
So the hypercall in hv_get_partition_id() should fail.
Michael
> +
> /*
> * Hyper-V expects to get crash register data or kmsg when
> * crash enlightment is available and system crashes. Set
> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
> index a7bbe504e4f3..98100466e0b2 100644
> --- a/include/asm-generic/mshyperv.h
> +++ b/include/asm-generic/mshyperv.h
> @@ -58,6 +58,7 @@ 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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