RE: [PATCH] PCI: hv: Replace retarget_msi_interrupt_params with hyperv_pcpu_input_arg

[Michael Kelley (LINUX)]

From: Dexuan Cui <decui@xxxxxxxxxxxxx> Sent: Saturday, April 8, 2023 2:11 PM
> 
> 4 commits are involved here:
> A (2016): commit 0de8ce3ee8e3 ("PCI: hv: Allocate physically contiguous hypercall
> params buffer")
> B (2017): commit be66b6736591 ("PCI: hv: Use page allocation for hbus structure")
> C (2019): commit 877b911a5ba0 ("PCI: hv: Avoid a kmemleak false positive caused by
> the hbus buffer")
> D (2018): commit 68bb7bfb7985 ("X86/Hyper-V: Enable IPI enlightenments")
> 
> Patch D introduced the per-CPU hypercall input page "hyperv_pcpu_input_arg"
> in 2018. With patch D, we no longer need the per-Hyper-V-PCI-bus hypercall
> input page "hbus->retarget_msi_interrupt_params" that was added in patch A,
> and the issue addressed by patch B is no longer an issue, and we can also
> get rid of patch C.
> 
> The change here is required for PCI device assignment to work for
> Confidential VMs (CVMs), because otherwise we would have to call
> set_memory_decrypted() for "hbus->retarget_msi_interrupt_params" before
> calling the hypercall HVCALL_RETARGET_INTERRUPT.

Well, not all CVMs.  It's not required for SEV-SNP vTOM VMs on Hyper-V because
of the paravisor.  Is it more accurate to say "for Confidential VMs (CVMs) running
without a paravisor"?

Otherwise,

Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>

> 
> Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
> ---
>  drivers/pci/controller/pci-hyperv.c | 48 +++++------------------------
>  1 file changed, 7 insertions(+), 41 deletions(-)
> 
> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> index 337f3b4a04fc0..bc32662c6bb7f 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -508,20 +508,11 @@ struct hv_pcibus_device {
>  	struct msi_domain_info msi_info;
>  	struct irq_domain *irq_domain;
> 
> -	spinlock_t retarget_msi_interrupt_lock;
> -
>  	struct workqueue_struct *wq;
> 
>  	/* Highest slot of child device with resources allocated */
>  	int wslot_res_allocated;
>  	bool use_calls; /* Use hypercalls to access mmio cfg space */
> -
> -	/* hypercall arg, must not cross page boundary */
> -	struct hv_retarget_device_interrupt retarget_msi_interrupt_params;
> -
> -	/*
> -	 * Don't put anything here: retarget_msi_interrupt_params must be last
> -	 */
>  };
> 
>  /*
> @@ -645,9 +636,9 @@ static void hv_arch_irq_unmask(struct irq_data *data)
>  	hbus = container_of(pbus->sysdata, struct hv_pcibus_device, sysdata);
>  	int_desc = data->chip_data;
> 
> -	spin_lock_irqsave(&hbus->retarget_msi_interrupt_lock, flags);
> +	local_irq_save(flags);
> 
> -	params = &hbus->retarget_msi_interrupt_params;
> +	params = *this_cpu_ptr(hyperv_pcpu_input_arg);
>  	memset(params, 0, sizeof(*params));
>  	params->partition_id = HV_PARTITION_ID_SELF;
>  	params->int_entry.source = HV_INTERRUPT_SOURCE_MSI;
> @@ -680,7 +671,7 @@ static void hv_arch_irq_unmask(struct irq_data *data)
> 
>  		if (!alloc_cpumask_var(&tmp, GFP_ATOMIC)) {
>  			res = 1;
> -			goto exit_unlock;
> +			goto out;
>  		}
> 
>  		cpumask_and(tmp, dest, cpu_online_mask);
> @@ -689,7 +680,7 @@ static void hv_arch_irq_unmask(struct irq_data *data)
> 
>  		if (nr_bank <= 0) {
>  			res = 1;
> -			goto exit_unlock;
> +			goto out;
>  		}
> 
>  		/*
> @@ -708,8 +699,8 @@ static void hv_arch_irq_unmask(struct irq_data *data)
>  	res = hv_do_hypercall(HVCALL_RETARGET_INTERRUPT | (var_size << 17),
>  			      params, NULL);
> 
> -exit_unlock:
> -	spin_unlock_irqrestore(&hbus->retarget_msi_interrupt_lock, flags);
> +out:
> +	local_irq_restore(flags);
> 
>  	/*
>  	 * During hibernation, when a CPU is offlined, the kernel tries
> @@ -3598,35 +3589,11 @@ static int hv_pci_probe(struct hv_device *hdev,
>  	bool enter_d0_retry = true;
>  	int ret;
> 
> -	/*
> -	 * hv_pcibus_device contains the hypercall arguments for retargeting in
> -	 * hv_irq_unmask(). Those must not cross a page boundary.
> -	 */
> -	BUILD_BUG_ON(sizeof(*hbus) > HV_HYP_PAGE_SIZE);
> -
>  	bridge = devm_pci_alloc_host_bridge(&hdev->device, 0);
>  	if (!bridge)
>  		return -ENOMEM;
> 
> -	/*
> -	 * With the recent 59bb47985c1d ("mm, sl[aou]b: guarantee natural
> -	 * alignment for kmalloc(power-of-two)"), kzalloc() is able to allocate
> -	 * a 4KB buffer that is guaranteed to be 4KB-aligned. Here the size and
> -	 * alignment of hbus is important because hbus's field
> -	 * retarget_msi_interrupt_params must not cross a 4KB page boundary.
> -	 *
> -	 * Here we prefer kzalloc to get_zeroed_page(), because a buffer
> -	 * allocated by the latter is not tracked and scanned by kmemleak, and
> -	 * hence kmemleak reports the pointer contained in the hbus buffer
> -	 * (i.e. the hpdev struct, which is created in new_pcichild_device() and
> -	 * is tracked by hbus->children) as memory leak (false positive).
> -	 *
> -	 * If the kernel doesn't have 59bb47985c1d, get_zeroed_page() *must* be
> -	 * used to allocate the hbus buffer and we can avoid the kmemleak false
> -	 * positive by using kmemleak_alloc() and kmemleak_free() to ask
> -	 * kmemleak to track and scan the hbus buffer.
> -	 */
> -	hbus = kzalloc(HV_HYP_PAGE_SIZE, GFP_KERNEL);
> +	hbus = kzalloc(sizeof(*hbus), GFP_KERNEL);
>  	if (!hbus)
>  		return -ENOMEM;
> 
> @@ -3683,7 +3650,6 @@ static int hv_pci_probe(struct hv_device *hdev,
>  	INIT_LIST_HEAD(&hbus->dr_list);
>  	spin_lock_init(&hbus->config_lock);
>  	spin_lock_init(&hbus->device_list_lock);
> -	spin_lock_init(&hbus->retarget_msi_interrupt_lock);
>  	hbus->wq = alloc_ordered_workqueue("hv_pci_%x", 0,
>  					   hbus->bridge->domain_nr);
>  	if (!hbus->wq) {
> --
> 2.25.1