Re: [PATCH V6 3/5] hyper-v: Enable swiotlb bounce buffer for Isolation VM

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On 12/10/2021 9:25 PM, Tianyu Lan wrote:
@@ -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?

Sorry. ignore the previous statement. These codes doesn't depend on CONFIG_HYPERV.

How about making these code under #ifdef CONFIG_X86_64 or CONFIG_SWIOTLB?



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