Re: [PATCH v2 5/6] PCI: hv: Use hv_hvcall_*() to set up hypercall arguments

[Nuno Das Neves <nunodasneves@linux.microsoft.com>]

On 3/12/2025 11:19 PM, mhkelley58@gmail.com wrote:
> From: Michael Kelley <mhklinux@outlook.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().
> 
> Signed-off-by: Michael Kelley <mhklinux@outlook.com>
> Acked-by: Bjorn Helgaas <bhelgaas@google.com>
> ---
> 
> Notes:
>     Changes in v2:
>     * In hv_arch_irq_unmask(), added check of the number of computed banks
>       in the hv_vpset against the batch_size. Since an hv_vpset currently
>       represents a maximum of 4096 CPUs, the hv_vpset size does not exceed
>       512 bytes and there should always be sufficent space. But do the
>       check just in case something changes. [Nuno Das Neves]
> 
>  drivers/pci/controller/pci-hyperv.c | 18 ++++++++----------
>  include/hyperv/hvgdk_mini.h         |  2 +-
>  2 files changed, 9 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> index ac27bda5ba26..82ac0e09943b 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -622,7 +622,7 @@ static void hv_arch_irq_unmask(struct irq_data *data)
>  	struct pci_dev *pdev;
>  	unsigned long flags;
>  	u32 var_size = 0;
> -	int cpu, nr_bank;
> +	int cpu, nr_bank, batch_size;
>  	u64 res;
>  
>  	dest = irq_data_get_effective_affinity_mask(data);
> @@ -638,8 +638,8 @@ static void hv_arch_irq_unmask(struct irq_data *data)
>  
>  	local_irq_save(flags);
>  
> -	params = *this_cpu_ptr(hyperv_pcpu_input_arg);
> -	memset(params, 0, sizeof(*params));
> +	batch_size = hv_hvcall_in_array(&params, sizeof(*params),
> +					sizeof(params->int_target.vp_set.bank_contents[0]));
>  	params->partition_id = HV_PARTITION_ID_SELF;
>  	params->int_entry.source = HV_INTERRUPT_SOURCE_MSI;
>  	params->int_entry.msi_entry.address.as_uint32 = int_desc->address & 0xffffffff;
> @@ -671,7 +671,7 @@ static void hv_arch_irq_unmask(struct irq_data *data)
>  		nr_bank = cpumask_to_vpset(&params->int_target.vp_set, tmp);
>  		free_cpumask_var(tmp);
>  
> -		if (nr_bank <= 0) {
> +		if (nr_bank <= 0 || nr_bank > batch_size) {
>  			res = 1;
>  			goto out;
>  		}
> @@ -1034,11 +1034,9 @@ static void hv_pci_read_mmio(struct device *dev, phys_addr_t gpa, int size, u32
>  
>  	/*
>  	 * Must be called with interrupts disabled so it is safe
> -	 * to use the per-cpu input argument page.  Use it for
> -	 * both input and output.
> +	 * to use the per-cpu argument page.
>  	 */
> -	in = *this_cpu_ptr(hyperv_pcpu_input_arg);
> -	out = *this_cpu_ptr(hyperv_pcpu_input_arg) + sizeof(*in);
> +	hv_hvcall_inout(&in, sizeof(*in), &out, sizeof(*out));
>  	in->gpa = gpa;
>  	in->size = size;
>  
> @@ -1067,9 +1065,9 @@ static void hv_pci_write_mmio(struct device *dev, phys_addr_t gpa, int size, u32
>  
>  	/*
>  	 * Must be called with interrupts disabled so it is safe
> -	 * to use the per-cpu input argument memory.
> +	 * to use the per-cpu argument page.
>  	 */
> -	in = *this_cpu_ptr(hyperv_pcpu_input_arg);
> +	hv_hvcall_in_array(&in, sizeof(*in), sizeof(in->data[0]));
>  	in->gpa = gpa;
>  	in->size = size;
>  	switch (size) {
> diff --git a/include/hyperv/hvgdk_mini.h b/include/hyperv/hvgdk_mini.h
> index 70e5d7ee40c8..cb25ac1e3ac5 100644
> --- a/include/hyperv/hvgdk_mini.h
> +++ b/include/hyperv/hvgdk_mini.h
> @@ -1342,7 +1342,7 @@ struct hv_mmio_write_input {
>  	u64 gpa;
>  	u32 size;
>  	u32 reserved;
> -	u8 data[HV_HYPERCALL_MMIO_MAX_DATA_LENGTH];
> +	u8 data[];

As with the prior patch, I don't think this is worth changing. The
code in hv_pci_write_mmio() is more complicated as a result, and
changing the array means the struct no longer matches the Hyper-V
struct 1:1.

Thanks
Nuno

>  } __packed;
>  
>  #endif /* _HV_HVGDK_MINI_H */