virtio: improve virtiofs and VirtioProxy performance with per-device SWIOTLB pool#40654
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benhillis wants to merge 1 commit into
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virtio: improve virtiofs and VirtioProxy performance with per-device SWIOTLB pool#40654benhillis wants to merge 1 commit into
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Pull request overview
This PR introduces an end-to-end “guest-published SWIOTLB pool” handshake: the Linux guest (WSL kernel) publishes an hv_pci SWIOTLB pool (base/size), the Windows side reads and forwards it, and device creation paths pass a swiotlb=... token to wsldevicehost so it can program a matching per-device aperture (virtio-fs and virtio-net).
Changes:
- Add guest→host capability plumbing for hv_pci SWIOTLB pool (new init/WSLC messages, service/session forwarding, and telemetry logging).
- Thread a cached
swiotlb=0x{base:x},{size}token into virtio device creation (VirtioFS shares and VirtioProxy/virtio-net). - Add
.wslconfigparsing/validation and user-facing localization for SWIOTLB/virtio-related warnings, plus unit test coverage.
Reviewed changes
Copilot reviewed 23 out of 23 changed files in this pull request and generated 2 comments.
Show a summary per file
| File | Description |
|---|---|
| test/windows/UnitTests.cpp | Adds unit tests validating .wslconfig experimental.swiotlb parsing and rejection of malformed values. |
| src/windows/wslcsession/WSLCVirtualMachine.h | Adds per-VM guest capability fields and a ReadGuestCapabilities() step. |
| src/windows/wslcsession/WSLCVirtualMachine.cpp | Implements guest capability query over the init channel and forwards to the service via COM. |
| src/windows/service/inc/wslc.idl | Adds WSLCGuestCapabilities struct and a new ApplyGuestCapabilities method on IWSLCVirtualMachine. |
| src/windows/service/exe/WslCoreVm.h | Stores hv_pci SWIOTLB base/size and a cached SWIOTLB device-options token. |
| src/windows/service/exe/WslCoreVm.cpp | Reads hv_pci SWIOTLB info, caches formatted token, passes it to VirtioNetworking, and appends it to VirtioFS share options. |
| src/windows/service/exe/HcsVirtualMachine.h | Stores a cached SWIOTLB token for WSLC virtio device creation paths. |
| src/windows/service/exe/HcsVirtualMachine.cpp | Computes default SWIOTLB request size, passes it to kernel cmdline helper, threads token into VirtioNetworking/AddShare, and implements ApplyGuestCapabilities. |
| src/windows/common/WslCoreConfig.h | Adds experimental.swiotlb key constant and config field SwiotlbSizeBytes. |
| src/windows/common/WslCoreConfig.cpp | Parses experimental.swiotlb, validates virtio dependencies, and computes default SWIOTLB sizing only when relevant virtio paths are enabled. |
| src/windows/common/VirtioNetworking.h | Extends ctor to accept SWIOTLB token to pass into virtio-net device creation. |
| src/windows/common/VirtioNetworking.cpp | Passes SWIOTLB token into virtio-net/loopback device creation calls. |
| src/windows/common/helpers.hpp | Extends AppendCommonKernelCommandLine to accept SWIOTLB size and adds ComputeDefaultSwiotlbConfig. |
| src/windows/common/helpers.cpp | Appends swiotlb=force hv_pci_swiotlb=<bytes> when requested; implements default sizing helper. |
| src/windows/common/GuestDeviceManager.h | Adds m_vmIdOption member for device-host ownership tagging. |
| src/windows/common/GuestDeviceManager.cpp | Appends a vm_id= option to device share names and avoids adding an empty options delimiter. |
| src/shared/inc/lxinitshared.h | Adds WSLC message types for guest capability query and adds SWIOTLB fields to LX_INIT_GUEST_CAPABILITIES. |
| src/linux/init/WSLCInit.cpp | Handles WSLC guest capability query by reading hv_pci SWIOTLB sysfs and returning base/size. |
| src/linux/init/util.h | Introduces HvPciSwiotlbPool and declaration for reading the sysfs pool info. |
| src/linux/init/util.cpp | Implements sysfs reads for swiotlb_base/swiotlb_size with a safe fallback to zeros. |
| src/linux/init/main.cpp | Includes SWIOTLB base/size in LX_INIT_GUEST_CAPABILITIES sent to the service. |
| packages.config | Bumps Microsoft.WSL.DeviceHost and Microsoft.WSL.Kernel packages for SWIOTLB aperture/handshake support. |
| localization/strings/en-US/Resources.resw | Adds new localized messages for VirtioProxy fallback and missing-kernel-patch SWIOTLB warning. |
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| if (m_hvPciSwiotlbBase != 0 && m_hvPciSwiotlbSize != 0) | ||
| { | ||
| m_swiotlbOption = std::format(L"swiotlb=0x{:x},{}", m_hvPciSwiotlbBase, m_hvPciSwiotlbSize); | ||
| } | ||
| else if (m_vmConfig.SwiotlbSizeBytes != 0) |
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asherkariv
previously approved these changes
May 27, 2026
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| // swiotlb device-options token. Passing zero for both means the guest kernel does not | ||
| // support hv_pci swiotlb; the service then omits the token and emits a user warning. |
…SWIOTLB pool
Improves virtiofs and VirtioProxy performance by giving each virtio
device its own SWIOTLB aperture instead of sharing a single global
pool. The guest kernel reserves a contiguous physical range at boot,
publishes the (base, size), and the host programs a matching
per-device aperture in wsldevicehost.
1. The WSL kernel allocates a contiguous range at boot
(alloc_contig_pages with __GFP_DMA32 | __GFP_ZERO) and exposes
the chosen physical (base, size) under
/sys/bus/vmbus/drivers/hv_pci/swiotlb_{base,size}
2. mini_init (WSL2) and the WSLC init handler read those sysfs files
and return the values in LX_INIT_GUEST_CAPABILITIES and
WSLC_GET_GUEST_CAPABILITIES_RESULT respectively.
3. WslCoreVm::ReadGuestCapabilities and
WSLCVirtualMachine::ReadGuestCapabilities capture the values.
WSLC forwards them to wslservice via the new
HcsVirtualMachine::ApplyGuestCapabilities IDL method (with a
WSLCGuestCapabilities struct so future kernel-published values
can be added without bumping the interface IID).
4. Both VM owners format "swiotlb=0x{base:x},{size}" once into
m_swiotlbOption and pass it verbatim to AddGuestDevice /
AddSharePath for every virtiofs share and virtio-net adapter
(VirtioProxy networking). wsldevicehost consumes the token and
creates the per-device SWIOTLB aperture.
If the kernel does not publish the sysfs files (older kernel) both
values come back as zero, the host omits the device-options token,
and the WSL2 path emits a one-time user warning via
MessageSwiotlbKernelUnsupported so users understand why performance
is degraded. (The WSLC path always uses the bundled kernel, so the
warning does not apply there.)
Other changes:
* Bump Microsoft.WSL.Kernel to 6.18.26.3-1, which is the first
official kernel that publishes the hv_pci swiotlb_{base,size}
sysfs files this PR consumes.
* Bump Microsoft.WSL.DeviceHost to 1.2.29-0 for the device-side
SWIOTLB aperture support.
* Default pool sizing moves to helpers::ComputeDefaultSwiotlbConfig
and is only requested on the kernel command line when a virtio
device that needs bounce buffers (VirtioFs / Virtio9p /
VirtioProxy) is in use.
* Telemetry: emit GuestKernelInfo / WSLCReadGuestCapabilities /
WSLCApplyGuestCapabilities events with the kernel-chosen base
and size so we can validate the handshake in CI.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Improves virtiofs and VirtioProxy performance by giving each virtio device its own SWIOTLB aperture instead of sharing a single global pool. The guest kernel reserves a contiguous physical range at boot, publishes the (base, size), and the host programs a matching per-device aperture in wsldevicehost.
Handshake:
alloc_contig_pages,__GFP_DMA32 | __GFP_ZERO) and exposes it under/sys/bus/vmbus/drivers/hv_pci/swiotlb_{base,size}.mini_init(WSL2) and the WSLC init handler read the sysfs files and return the values inLX_INIT_GUEST_CAPABILITIES/WSLC_GET_GUEST_CAPABILITIES_RESULT.WslCoreVm::ReadGuestCapabilitiesandWSLCVirtualMachine::ReadGuestCapabilitiescapture them. WSLC forwards them via the newHcsVirtualMachine::ApplyGuestCapabilitiesIDL method (taking aWSLCGuestCapabilitiesstruct).swiotlb=0x{base:x},{size}once intom_swiotlbOptionand pass it toAddGuestDevice/AddSharePathfor every virtiofs share and virtio-net adapter (VirtioProxy networking).Bumps
Microsoft.WSL.Kernelto 6.18.26.3-1 (first official kernel with the patch) andMicrosoft.WSL.DeviceHostto 1.2.29-0 (consumes the swiotlb device-options token).