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fix(openhcl_boot): enable swiotlb for VBS-isolated VMs #3752

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fix(openhcl_boot): enable swiotlb for VBS-isolated VMs #3752

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18 changes: 6 additions & 12 deletions openhcl/openhcl_boot/src/main.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -226,16 +226,10 @@ fn build_kernel_command_line(
write!(cmdline, "{p} ")?;
}

const HARDWARE_ISOLATED_KERNEL_PARAMETERS: &[&str] = &[
// Even with iommu=off, the SWIOTLB is still allocated on AARCH64
// (iommu=off ignored entirely), and CVMs (memory encryption forces it
// on). Set it to a single area in 8MB. The first parameter controls the
// area size in slabs (2KB per slab), the second controls the number of
// areas (default is # of CPUs).
//
// This is set to 8MB on hardware isolated VMs since there are some
// scenarios, such as provisioning over DVD, which require a larger size
// since the buffer is being used.
// Set SWIOTLB to 8MB for all isolated VMs. Hardware-isolated VMs
// (TDX/SNP) need it for memory encryption, and VBS-isolated VMs need
// it because VTL2 private memory is not accessible from VTL0.
const ISOLATED_KERNEL_PARAMETERS: &[&str] = &[
"swiotlb=4096,1",
];

Expand All @@ -247,8 +241,8 @@ fn build_kernel_command_line(
"swiotlb=1,1",
];

if params.isolation_type.is_hardware_isolated() {
for p in HARDWARE_ISOLATED_KERNEL_PARAMETERS {
if params.isolation_type != IsolationType::None {

@smalis-msft smalis-msft Jun 16, 2026

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I think IsolationType has an is_isolated helper we should use instead.

for p in ISOLATED_KERNEL_PARAMETERS {
write!(cmdline, "{p} ")?;
}
} else {
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