On 12/10/2021 4:09 AM, Michael Kelley (LINUX) wrote:

quoted

@@ -319,8 +320,16 @@ static void __init ms_hyperv_init_platform(void)
  		pr_info("Hyper-V: Isolation Config: Group A 0x%x, Group B 0x%x\n",
  			ms_hyperv.isolation_config_a, ms_hyperv.isolation_config_b);

-		if (hv_get_isolation_type() == HV_ISOLATION_TYPE_SNP)
+		if (hv_get_isolation_type() == HV_ISOLATION_TYPE_SNP) {
  			static_branch_enable(&isolation_type_snp);
+			swiotlb_unencrypted_base = ms_hyperv.shared_gpa_boundary;
+		}
+
+		/*
+		 * Enable swiotlb force mode in Isolation VM to
+		 * use swiotlb bounce buffer for dma transaction.
+		 */
+		swiotlb_force = SWIOTLB_FORCE;

I'm good with this approach that directly updates the swiotlb settings here

rather than in IOMMU initialization code.  It's a lot more straightforward.

However, there's an issue if building for X86_32 without PAE, in that the
swiotlb module may not be built, resulting in compile and link errors.  The
swiotlb.h file needs to be updated to provide a stub function for
swiotlb_update_mem_attributes().   swiotlb_unencrypted_base probably
needs wrapper functions to get/set it, which can be stubs when
CONFIG_SWIOTLB is not set.  swiotlb_force is a bit of a mess in that it already
has a stub definition that assumes it will only be read, and not set.  A bit of
thinking will be needed to sort that out.

It's ok to fix the issue via selecting swiotlb when CONFIG_HYPERV is
set?

quoted

  	}

  	if (hv_max_functions_eax >= HYPERV_CPUID_NESTED_FEATURES) {

diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index b823311eac79..1f037e114dc8 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h

@@ -1726,6 +1726,14 @@ 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));
+#if IS_ENABLED(CONFIG_HYPERV)
+int __init hyperv_swiotlb_detect(void);
+#else
+static inline int __init hyperv_swiotlb_detect(void)
+{
+	return 0;
+}
+#endif

I don't think hyperv_swiotlb_detect() is used any longer, so this change
should be dropped.

Yes, will update.