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

Michael Kelley (LINUX)
2023-04-11T17:27:49Z

From: Dexuan Cui <decui@microsoft.com> 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@microsoft.com>

>
> Signed-off-by: Dexuan Cui <decui@microsoft.com>
> ---
> 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