Hello, this series introduce a new hypercall ABI proposal (x86 only for now).
The current Xen ABI has some shortcommings : First, the hypercall parameters are usually pointers that point to a structure in guest memory, this pointer is usually a virtual address. It causes various issues as : - you need to define a format for these structures which is currently C structures, but it complicates support with non LP64 platforms (e.g Windows) or other programming languages (e.g Rust, where solutions are hard to come with) - the translation from virtual address to machine physical address is very expensive as you need to translate the GVA to GPA, and then GPA to HPA each time you want to access a virtual address - such virtual addresses are not readable under confidential computing guests which makes such new ABI required. Another issue is that all possible Xen hypercalls are exposed through this single interface, it makes hardening the hypervisor more complicated as you need to permission check on a per-hypercall basis (e.g through XSM) instead of having a minimal strict safe-for-guest-use set of operations. The current ABI allows the guest to modify its physmap; this is notably used for mapping the shared info, grant table and ballooning. While we could make that work for confidential guests. It comes with its own set of problems, and in order to simplify the memory management, this series come with a proposal for mapping these specific pages in advance and telling the guest the location. That helps reducing the scope of this new ABI. Ballooning implementation hasn't been fully considered yet. This series propose a new hypercall interface designed for use by guests kernels with high performance (low hypercall overhead) and confidential computing environments (notably AMD SEV) compatibility in mind. It currently only supports x86 long mode (64-bits) due to specific register requirements. It doesn't aim to entirely replace the current ABI, but to propose a alternative one that could be used by guests as a fast-path ABI or for confidential computing guests. This new ABI maps into current many operations (with some limitations), a tool is provided to generate C stubs using the yaml specification. These C stubs reuse the existing hypercall structures to ease adding support for this ABI in guests. You can find some example generated headers in Linux SEV WIP branch [1]. [1] https://github.com/xcp-ng/linux/tree/xen-sev-6.14/include/xen/interface/fastabi Teddy Astie (9): x86/hvm: Use direct structures instead of guest handles common: Isolate XENVER_get_features into a separate function common/grant_table: Use direct structures instead of guest handles hvm: Introduce "fixed memory layout" feature docs/x86: Introduce FastABI sched: Extract do_poll main logic into vcpu_poll x86/hvm: Introduce FastABI implementation hvm: Introduce XEN_HVM_MEMMAP_TYPE_HOTPLUG_ZONE tools: Introduce abi-tool docs/guest-guide/x86/fastabi.pandoc | 50 +++++ .../x86/fixed-memory-layout.pandoc | 24 ++ docs/guest-guide/x86/index.rst | 2 + tools/include/xen-tools/common-macros.h | 4 + tools/libs/guest/xg_dom_x86.c | 84 +++++++ tools/libs/light/libxl_create.c | 1 + tools/libs/light/libxl_types.idl | 1 + tools/libs/light/libxl_x86.c | 71 ++++++ tools/xl/xl_parse.c | 1 + xen/abi/event_channel.yml | 130 +++++++++++ xen/abi/grant_table.yml | 46 ++++ xen/abi/hvm.yml | 50 +++++ xen/abi/memory.yml | 11 + xen/abi/sched.yml | 48 ++++ xen/abi/vcpu.yml | 139 ++++++++++++ xen/abi/version.yml | 15 ++ xen/arch/x86/cpuid.c | 3 + xen/arch/x86/domain.c | 71 ++++++ xen/arch/x86/hvm/hvm.c | 205 +++++++++++++----- xen/arch/x86/hvm/hypercall.c | 22 ++ xen/arch/x86/include/asm/fastabi.h | 17 ++ xen/common/Kconfig | 6 + xen/common/Makefile | 1 + xen/common/domain.c | 179 +++++++++++++++ xen/common/event_channel.c | 199 +++++++++++++++++ xen/common/fastabi.c | 49 +++++ xen/common/grant_table.c | 112 +++++++--- xen/common/kernel.c | 117 ++++++---- xen/common/memory.c | 110 ++++++++++ xen/common/sched/core.c | 149 +++++++++++-- xen/include/public/arch-x86/cpuid.h | 4 + xen/include/public/arch-x86/hvm/start_info.h | 8 + xen/include/public/event_channel.h | 7 + xen/include/public/fastabi.h | 20 ++ xen/include/xen/fastabi.h | 21 ++ xen/tools/abi-tool/.gitignore | 1 + xen/tools/abi-tool/Cargo.lock | 145 +++++++++++++ xen/tools/abi-tool/Cargo.toml | 11 + xen/tools/abi-tool/src/abi.rs | 23 ++ xen/tools/abi-tool/src/c_lang.rs | 173 +++++++++++++++ xen/tools/abi-tool/src/main.rs | 17 ++ xen/tools/abi-tool/src/spec.rs | 61 ++++++ 42 files changed, 2265 insertions(+), 143 deletions(-) create mode 100644 docs/guest-guide/x86/fastabi.pandoc create mode 100644 docs/guest-guide/x86/fixed-memory-layout.pandoc create mode 100644 xen/abi/event_channel.yml create mode 100644 xen/abi/grant_table.yml create mode 100644 xen/abi/hvm.yml create mode 100644 xen/abi/memory.yml create mode 100644 xen/abi/sched.yml create mode 100644 xen/abi/vcpu.yml create mode 100644 xen/abi/version.yml create mode 100644 xen/arch/x86/include/asm/fastabi.h create mode 100644 xen/common/fastabi.c create mode 100644 xen/include/public/fastabi.h create mode 100644 xen/include/xen/fastabi.h create mode 100644 xen/tools/abi-tool/.gitignore create mode 100644 xen/tools/abi-tool/Cargo.lock create mode 100644 xen/tools/abi-tool/Cargo.toml create mode 100644 xen/tools/abi-tool/src/abi.rs create mode 100644 xen/tools/abi-tool/src/c_lang.rs create mode 100644 xen/tools/abi-tool/src/main.rs create mode 100644 xen/tools/abi-tool/src/spec.rs -- 2.50.1 Teddy Astie | Vates XCP-ng Developer XCP-ng & Xen Orchestra - Vates solutions web: https://vates.tech
