RE: [PATCH V3 11/13] HV/IOMMU: Enable swiotlb bounce buffer for Isolation VM

[Michael Kelley <mikelley@microsoft.com>]

From: Tianyu Lan <ltykernel@gmail.com> Sent: Monday, August 9, 2021 10:56 AM
> 
> Hyper-V Isolation VM requires bounce buffer support to copy
> data from/to encrypted memory and so enable swiotlb force
> mode to use swiotlb bounce buffer for DMA transaction.
> 
> In Isolation VM with AMD SEV, the bounce buffer needs to be
> accessed via extra address space which is above shared_gpa_boundary
> (E.G 39 bit address line) reported by Hyper-V CPUID ISOLATION_CONFIG.
> The access physical address will be original physical address +
> shared_gpa_boundary. The shared_gpa_boundary in the AMD SEV SNP
> spec is called virtual top of memory(vTOM). Memory addresses below
> vTOM are automatically treated as private while memory above
> vTOM is treated as shared.
> 
> Swiotlb bounce buffer code calls dma_map_decrypted()
> to mark bounce buffer visible to host and map it in extra
> address space. Populate dma memory decrypted ops with hv
> map/unmap function.
> 
> Hyper-V initalizes swiotlb bounce buffer and default swiotlb
> needs to be disabled. pci_swiotlb_detect_override() and
> pci_swiotlb_detect_4gb() enable the default one. To override
> the setting, hyperv_swiotlb_detect() needs to run before
> these detect functions which depends on the pci_xen_swiotlb_
> init(). Make pci_xen_swiotlb_init() depends on the hyperv_swiotlb
> _detect() to keep the order.
> 
> The map function vmap_pfn() can't work in the early place
> hyperv_iommu_swiotlb_init() and so initialize swiotlb bounce
> buffer in the hyperv_iommu_swiotlb_later_init().
> 
> Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
> ---
>  arch/x86/hyperv/ivm.c           | 28 ++++++++++++++
>  arch/x86/include/asm/mshyperv.h |  2 +
>  arch/x86/xen/pci-swiotlb-xen.c  |  3 +-
>  drivers/hv/vmbus_drv.c          |  3 ++
>  drivers/iommu/hyperv-iommu.c    | 65 +++++++++++++++++++++++++++++++++
>  include/linux/hyperv.h          |  1 +
>  6 files changed, 101 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
> index c13ec5560d73..0f05e4d6fc62 100644
> --- a/arch/x86/hyperv/ivm.c
> +++ b/arch/x86/hyperv/ivm.c
> @@ -265,3 +265,31 @@ int hv_set_mem_host_visibility(unsigned long addr, int numpages, bool visible)
> 
>  	return __hv_set_mem_host_visibility((void *)addr, numpages, visibility);
>  }
> +
> +/*
> + * hv_map_memory - map memory to extra space in the AMD SEV-SNP Isolation VM.
> + */
> +void *hv_map_memory(void *addr, unsigned long size)
> +{
> +	unsigned long *pfns = kcalloc(size / HV_HYP_PAGE_SIZE,
> +				      sizeof(unsigned long), GFP_KERNEL);
> +	void *vaddr;
> +	int i;
> +
> +	if (!pfns)
> +		return NULL;
> +
> +	for (i = 0; i < size / HV_HYP_PAGE_SIZE; i++)
> +		pfns[i] = virt_to_hvpfn(addr + i * HV_HYP_PAGE_SIZE) +
> +			(ms_hyperv.shared_gpa_boundary >> HV_HYP_PAGE_SHIFT);
> +
> +	vaddr = vmap_pfn(pfns, size / HV_HYP_PAGE_SIZE,	PAGE_KERNEL_IO);
> +	kfree(pfns);
> +
> +	return vaddr;
> +}

This function is manipulating page tables in the guest VM.  It is not involved
in communicating with Hyper-V, or passing PFNs to Hyper-V.  The pfn array
contains guest PFNs, not Hyper-V PFNs.  So it should use PAGE_SIZE
instead of HV_HYP_PAGE_SIZE, and similarly PAGE_SHIFT and virt_to_pfn().
If this code were ever to run on ARM64 in the future with PAGE_SIZE other
than 4 Kbytes, the use of PAGE_SIZE is correct choice.

> +
> +void hv_unmap_memory(void *addr)
> +{
> +	vunmap(addr);
> +}
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index a30c60f189a3..b247739f57ac 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -250,6 +250,8 @@ int hv_unmap_ioapic_interrupt(int ioapic_id, struct hv_interrupt_entry *entry);
>  int hv_mark_gpa_visibility(u16 count, const u64 pfn[],
>  			   enum hv_mem_host_visibility visibility);
>  int hv_set_mem_host_visibility(unsigned long addr, int numpages, bool visible);
> +void *hv_map_memory(void *addr, unsigned long size);
> +void hv_unmap_memory(void *addr);
>  void hv_sint_wrmsrl_ghcb(u64 msr, u64 value);
>  void hv_sint_rdmsrl_ghcb(u64 msr, u64 *value);
>  void hv_signal_eom_ghcb(void);
> diff --git a/arch/x86/xen/pci-swiotlb-xen.c b/arch/x86/xen/pci-swiotlb-xen.c
> index 54f9aa7e8457..43bd031aa332 100644
> --- a/arch/x86/xen/pci-swiotlb-xen.c
> +++ b/arch/x86/xen/pci-swiotlb-xen.c
> @@ -4,6 +4,7 @@
> 
>  #include <linux/dma-map-ops.h>
>  #include <linux/pci.h>
> +#include <linux/hyperv.h>
>  #include <xen/swiotlb-xen.h>
> 
>  #include <asm/xen/hypervisor.h>
> @@ -91,6 +92,6 @@ int pci_xen_swiotlb_init_late(void)
>  EXPORT_SYMBOL_GPL(pci_xen_swiotlb_init_late);
> 
>  IOMMU_INIT_FINISH(pci_xen_swiotlb_detect,
> -		  NULL,
> +		  hyperv_swiotlb_detect,
>  		  pci_xen_swiotlb_init,
>  		  NULL);
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 57bbbaa4e8f7..f068e22a5636 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -23,6 +23,7 @@
>  #include <linux/cpu.h>
>  #include <linux/sched/task_stack.h>
> 
> +#include <linux/dma-map-ops.h>
>  #include <linux/delay.h>
>  #include <linux/notifier.h>
>  #include <linux/panic_notifier.h>
> @@ -2081,6 +2082,7 @@ struct hv_device *vmbus_device_create(const guid_t *type,
>  	return child_device_obj;
>  }
> 
> +static u64 vmbus_dma_mask = DMA_BIT_MASK(64);
>  /*
>   * vmbus_device_register - Register the child device
>   */
> @@ -2121,6 +2123,7 @@ int vmbus_device_register(struct hv_device *child_device_obj)
>  	}
>  	hv_debug_add_dev_dir(child_device_obj);
> 
> +	child_device_obj->device.dma_mask = &vmbus_dma_mask;
>  	return 0;
> 
>  err_kset_unregister:
> diff --git a/drivers/iommu/hyperv-iommu.c b/drivers/iommu/hyperv-iommu.c
> index e285a220c913..01e874b3b43a 100644
> --- a/drivers/iommu/hyperv-iommu.c
> +++ b/drivers/iommu/hyperv-iommu.c
> @@ -13,14 +13,22 @@
>  #include <linux/irq.h>
>  #include <linux/iommu.h>
>  #include <linux/module.h>
> +#include <linux/hyperv.h>
> +#include <linux/io.h>
> 
>  #include <asm/apic.h>
>  #include <asm/cpu.h>
>  #include <asm/hw_irq.h>
>  #include <asm/io_apic.h>
> +#include <asm/iommu.h>
> +#include <asm/iommu_table.h>
>  #include <asm/irq_remapping.h>
>  #include <asm/hypervisor.h>
>  #include <asm/mshyperv.h>
> +#include <asm/swiotlb.h>
> +#include <linux/dma-map-ops.h>
> +#include <linux/dma-direct.h>
> +#include <linux/set_memory.h>
> 
>  #include "irq_remapping.h"
> 
> @@ -36,6 +44,9 @@
>  static cpumask_t ioapic_max_cpumask = { CPU_BITS_NONE };
>  static struct irq_domain *ioapic_ir_domain;
> 
> +static unsigned long hyperv_io_tlb_size;
> +static void *hyperv_io_tlb_start;
> +
>  static int hyperv_ir_set_affinity(struct irq_data *data,
>  		const struct cpumask *mask, bool force)
>  {
> @@ -337,4 +348,58 @@ static const struct irq_domain_ops hyperv_root_ir_domain_ops = {
>  	.free = hyperv_root_irq_remapping_free,
>  };
> 
> +void __init hyperv_iommu_swiotlb_init(void)
> +{
> +	unsigned long bytes;
> +
> +	/*
> +	 * Allocate Hyper-V swiotlb bounce buffer at early place
> +	 * to reserve large contiguous memory.
> +	 */
> +	hyperv_io_tlb_size = 256 * 1024 * 1024;

A hard coded size here seems problematic.   The memory size of
Isolated VMs can vary by orders of magnitude.  I see that
xen_swiotlb_init() uses swiotlb_size_or_default(), which at least
pays attention to the value specified on the kernel boot line.

Another example is sev_setup_arch(), which in the native case sets
the size to 6% of main memory, with a max of 1 Gbyte.  This is
the case that's closer to Isolated VMs, so doing something
similar could be a good approach.

> +	hyperv_io_tlb_start =
> +			memblock_alloc_low(
> +				  PAGE_ALIGN(hyperv_io_tlb_size),
> +				  HV_HYP_PAGE_SIZE);
> +
> +	if (!hyperv_io_tlb_start) {
> +		pr_warn("Fail to allocate Hyper-V swiotlb buffer.\n");
> +		return;
> +	}
> +}
> +
> +int __init hyperv_swiotlb_detect(void)
> +{
> +	if (hypervisor_is_type(X86_HYPER_MS_HYPERV)
> +	    && hv_is_isolation_supported()) {
> +		/*
> +		 * Enable swiotlb force mode in Isolation VM to
> +		 * use swiotlb bounce buffer for dma transaction.
> +		 */
> +		swiotlb_force = SWIOTLB_FORCE;
> +
> +		dma_memory_generic_decrypted_ops.map = hv_map_memory;
> +		dma_memory_generic_decrypted_ops.unmap = hv_unmap_memory;
> +		return 1;
> +	}
> +
> +	return 0;
> +}
> +
> +void __init hyperv_iommu_swiotlb_later_init(void)
> +{
> +	/*
> +	 * Swiotlb bounce buffer needs to be mapped in extra address
> +	 * space. Map function doesn't work in the early place and so
> +	 * call swiotlb_late_init_with_tbl() here.
> +	 */
> +	if (swiotlb_late_init_with_tbl(hyperv_io_tlb_start,
> +				       hyperv_io_tlb_size >> IO_TLB_SHIFT))
> +		panic("Fail to initialize hyperv swiotlb.\n");
> +}
> +
> +IOMMU_INIT_FINISH(hyperv_swiotlb_detect,
> +		  NULL, hyperv_iommu_swiotlb_init,
> +		  hyperv_iommu_swiotlb_later_init);
> +
>  #endif
> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
> index 90b542597143..83fa567ad594 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -1744,6 +1744,7 @@ int hyperv_write_cfg_blk(struct pci_dev *dev, void *buf, unsigned int len,
>  int hyperv_reg_block_invalidate(struct pci_dev *dev, void *context,
>  				void (*block_invalidate)(void *context,
>  							 u64 block_mask));
> +int __init hyperv_swiotlb_detect(void);
> 
>  struct hyperv_pci_block_ops {
>  	int (*read_block)(struct pci_dev *dev, void *buf, unsigned int buf_len,
> --
> 2.25.1