linux-kernel - Re: [PATCH 3/7] x86/hyperv: Use hv_hvcall_*() to set up hypercall arguments -- part 1

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Message-ID: <f9b3d2b7-59d6-42b7-b0eb-d26be3405b22@linux.microsoft.com>
Date: Thu, 27 Feb 2025 13:07:54 -0800
From: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
To: mhklinux@...look.com, kys@...rosoft.com, haiyangz@...rosoft.com,
 wei.liu@...nel.org, decui@...rosoft.com, tglx@...utronix.de,
 mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
 lpieralisi@...nel.org, kw@...ux.com, manivannan.sadhasivam@...aro.org,
 robh@...nel.org, bhelgaas@...gle.com, arnd@...db.de
Cc: x86@...nel.org, linux-hyperv@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
 linux-arch@...r.kernel.org
Subject: Re: [PATCH 3/7] x86/hyperv: Use hv_hvcall_*() to set up hypercall
 arguments -- part 1

On 2/26/2025 12:06 PM, mhkelley58@...il.com wrote:
> From: Michael Kelley <mhklinux@...look.com>
> 
> Update hypercall call sites to use the new hv_hvcall_*() functions
> to set up hypercall arguments. Since these functions zero the
> fixed portion of input memory, remove now redundant calls to memset()
> and explicit zero'ing of input fields.
> 
> Signed-off-by: Michael Kelley <mhklinux@...look.com>
> ---
>  arch/x86/hyperv/hv_apic.c   |  6 ++----
>  arch/x86/hyperv/hv_init.c   |  5 +----
>  arch/x86/hyperv/hv_vtl.c    |  8 ++------
>  arch/x86/hyperv/irqdomain.c | 10 ++++------
>  4 files changed, 9 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/x86/hyperv/hv_apic.c b/arch/x86/hyperv/hv_apic.c
> index f022d5f64fb6..c16f81dd36fc 100644
> --- a/arch/x86/hyperv/hv_apic.c
> +++ b/arch/x86/hyperv/hv_apic.c
> @@ -115,14 +115,12 @@ static bool __send_ipi_mask_ex(const struct cpumask *mask, int vector,
>  		return false;
>  
>  	local_irq_save(flags);
> -	ipi_arg = *this_cpu_ptr(hyperv_pcpu_input_arg);
> -
> +	hv_hvcall_in_array(&ipi_arg, sizeof(*ipi_arg),
> +				sizeof(ipi_arg->vp_set.bank_contents[0]));
I think the returned "batch size" should be checked to ensure it is not too small to hold the
variable-sized part of the header.

>  	if (unlikely(!ipi_arg))
>  		goto ipi_mask_ex_done;
>  
While here, is this check really needed? If so, maybe a check for the percpu page(s) could be
baked into hv_hvcall_inout_array()?

>  	ipi_arg->vector = vector;
> -	ipi_arg->reserved = 0;
> -	ipi_arg->vp_set.valid_bank_mask = 0;
>  
>  	/*
>  	 * Use HV_GENERIC_SET_ALL and avoid converting cpumask to VP_SET
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index ddeb40930bc8..c5c9511cb7ed 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -400,13 +400,10 @@ static u8 __init get_vtl(void)
>  	u64 ret;
>  
>  	local_irq_save(flags);
> -	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
> -	output = *this_cpu_ptr(hyperv_pcpu_output_arg);
>  
> -	memset(input, 0, struct_size(input, names, 1));
> +	hv_hvcall_inout(&input, sizeof(*input), &output, sizeof(*output));

This doesn't look right, this is a rep hypercall taking an array of register names
and outputting an array of register values.

hv_hvcall_inout_array() should be fully utilized (input and output arrays) here.

The current code may actually work, but it will overlap the input and output!

>  	input->partition_id = HV_PARTITION_ID_SELF;
>  	input->vp_index = HV_VP_INDEX_SELF;
> -	input->input_vtl.as_uint8 = 0;
>  	input->names[0] = HV_REGISTER_VSM_VP_STATUS;
>  
>  	ret = hv_do_hypercall(control, input, output);
> diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
> index 3f4e20d7b724..3dd27d548db6 100644
> --- a/arch/x86/hyperv/hv_vtl.c
> +++ b/arch/x86/hyperv/hv_vtl.c
<snip>
> @@ -185,13 +184,10 @@ static int hv_vtl_apicid_to_vp_id(u32 apic_id)
>  
>  	local_irq_save(irq_flags);
>  
> -	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
> -	memset(input, 0, sizeof(*input));
> +	hv_hvcall_inout(&input, sizeof(*input), &output, sizeof(*output));
This has the same issue as above - it is a rep hypercall so needs hv_hvcall_inout_array()

>  	input->partition_id = HV_PARTITION_ID_SELF;
>  	input->apic_ids[0] = apic_id;
>  
> -	output = *this_cpu_ptr(hyperv_pcpu_output_arg);
> -
>  	control = HV_HYPERCALL_REP_COMP_1 | HVCALL_GET_VP_ID_FROM_APIC_ID;
>  	status = hv_do_hypercall(control, input, output);
>  	ret = output[0];
> diff --git a/arch/x86/hyperv/irqdomain.c b/arch/x86/hyperv/irqdomain.c
> index 64b921360b0f..803b1a945c5c 100644
> --- a/arch/x86/hyperv/irqdomain.c
> +++ b/arch/x86/hyperv/irqdomain.c
> @@ -24,11 +24,11 @@ static int hv_map_interrupt(union hv_device_id device_id, bool level,
>  
>  	local_irq_save(flags);
>  
> -	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
> -	output = *this_cpu_ptr(hyperv_pcpu_output_arg);
> +	hv_hvcall_inout_array(&input, sizeof(*input),
> +			sizeof(input->interrupt_descriptor.target.vp_set.bank_contents[0]),
> +			&output, sizeof(*output), 0);
As noted before I think the batch size should be checked to ensure it is large enough.

Side note - it seems in this hypercall, nr_banks + 1 is used as the varhead size, which
counts the vp valid mask, but this is not the case in __send_ipi_mask_ex(). Do you happen
to know why that might be?

Thanks,
Nuno

>  
>  	intr_desc = &input->interrupt_descriptor;
> -	memset(input, 0, sizeof(*input));
>  	input->partition_id = hv_current_partition_id;
>  	input->device_id = device_id.as_uint64;
>  	intr_desc->interrupt_type = HV_X64_INTERRUPT_TYPE_FIXED;
<snip>