| Message ID | 20200922204910.7265-1-dbrazdil@google.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Independent per-CPU data section for nVHE | expand |
On Tue, 22 Sep 2020, David Brazdil wrote: > Introduce '.hyp.data..percpu' as part of ongoing effort to make nVHE > hyp code self-contained and independent of the rest of the kernel. The percpu subsystems point is to enable the use of special hardware instructions that can perform address calculation and a memory operation in one interruptible instruction. This is in particular useful to avoid higher overhead for memory management related counters because preempt disable/enable etc can be avoided. ARM cannot do that and thus has a LC/SC loop. This is a patchset for ARM64 so its not clear to me what kind of advantage there would be against a simple implementation that does a regular fetch from a base address with an offset. > Main benefits: > * independent nVHE per-CPU data section that can be unmapped from host, > * more robust linking of nVHE hyp code, > * no need for hyp-specific macros to access per-CPU variables. Maybe simply don't use percpu variables for your arm code? Those pointers to data will be much more indepedent of the rest of the kernel and allow a much higher degree of being self-contained.
On Tue, 22 Sep 2020 21:49:00 +0100, David Brazdil wrote: > Introduce '.hyp.data..percpu' as part of ongoing effort to make nVHE > hyp code self-contained and independent of the rest of the kernel. > > Main benefits: > * independent nVHE per-CPU data section that can be unmapped from host, > * more robust linking of nVHE hyp code, > * no need for hyp-specific macros to access per-CPU variables. > > [...] Applied to next, thanks! [01/10] kvm: arm64: Partially link nVHE hyp code, simplify HYPCOPY commit: ab25464bdabd45f283cc1194e332040f89071106 [02/10] kvm: arm64: Move nVHE hyp namespace macros to hyp_image.h commit: ce492a16ffb8814d9651c3fdafc363bfa1b01189 [03/10] kvm: arm64: Only define __kvm_ex_table for CONFIG_KVM commit: 3471ee06e33e413d7fa73c1aa3092e6e794b9e05 [04/10] kvm: arm64: Remove __hyp_this_cpu_read commit: 717cf94adb54095d14a6674baea73123188f2901 [05/10] kvm: arm64: Remove hyp_adr/ldr_this_cpu commit: ea391027d35546d9155f1350123b5af8bddec706 [06/10] kvm: arm64: Add helpers for accessing nVHE hyp per-cpu vars commit: 572494995bc3d282336bfd8162741929402910b9 [07/10] kvm: arm64: Duplicate arm64_ssbd_callback_required for nVHE hyp commit: df4c8214a18d202fa0ec221a001f640e020f7e44 [08/10] kvm: arm64: Create separate instances of kvm_host_data for VHE/nVHE commit: 2a1198c9b436402582f7beed57028044b819329c [09/10] kvm: arm64: Set up hyp percpu data for nVHE commit: 30c953911c4370bfb622ee1c2fcc7e78c84df800 [10/10] kvm: arm64: Remove unnecessary hyp mappings commit: a3bb9c3a00551726590137e3974495ce6cf6b758 Cheers, M.
Introduce '.hyp.data..percpu' as part of ongoing effort to make nVHE hyp code self-contained and independent of the rest of the kernel. Main benefits: * independent nVHE per-CPU data section that can be unmapped from host, * more robust linking of nVHE hyp code, * no need for hyp-specific macros to access per-CPU variables. The series is structured as follows: - patch 1: Improve existing hyp build rules. This could be sent and merged independently of per-CPU but this series builds on it. - patches 2-3: Minor cleanups. - patches 4-5: Replace hyp helpers for accessing per-CPU variables with common helpers modified to work correctly in hyp. Per-CPU variables can now be accessed with one API anywhere. - patches 6-8: Where VHE and nVHE use per-CPU variables defined in kernel proper, move their definitions to hyp/ where they are duplicated and owned by VHE/nVHE, respectively. Non-VHE hyp code now refers only to per-CPU variables defined in its source files. Helpers are added so that kernel proper can continue to access nVHE hyp variables, same way as it does with other nVHE symbols. - patches 9-10: Introduce '.hyp.data..percpu' ELF section and allocate memory for every CPU core during KVM init. All nVHE per-CPU state is now grouped together in ELF and in memory. Introducing a new per-CPU variable does not require adding new memory mappings any more. nVHE hyp code cannot accidentally refer to kernel-proper per-CPU data as it only has the pointer to its own per-CPU memory. Patches are rebased on v5.9-rc6 and available in branch 'topic/percpu-v4' at: https://android-kvm.googlesource.com/linux For maintainers: In case of interest, there are patches that remove the need for redefining macros under DEBUG_PREEMPT available at the same repo, branch 'topic/percpu-v3-debug-preempt'. Since they are non-trivial, I am not going to post them here so late in the 5.10 window. I plan to post them for 5.11 when they will also be useful for other patches. Changes v3 -> v4: * Drop patch that marked pages allocated for hyp reserved * Copy arm64_ssbd_callback_required at cpu_init_hyp_mode * Use read_sysreg in __hyp_my_cpu_offset * Simplify per-CPU region allocation code * Use same subsection name regex as other kernel linker scripts * Rename helper per-CPU macros * Add .gitignore for hyp linker script Changes v2 -> v3: * Use PERCPU_INPUT in hyp.ld instead of modifying PERCPU_SECTION * Only pass linker script once to LD (fix error message) * Renamed '.hyp.o' to '.nvhe.o' * Use __KVM_VHE_HYPERVISOR__ to select TPIDR_EL2 instead of alternatives * Move all prefixing-related macros to hyp_image.h Changes v1 -> v2: * partially link hyp code, add linker script David Brazdil (10): kvm: arm64: Partially link nVHE hyp code, simplify HYPCOPY kvm: arm64: Move nVHE hyp namespace macros to hyp_image.h kvm: arm64: Only define __kvm_ex_table for CONFIG_KVM kvm: arm64: Remove __hyp_this_cpu_read kvm: arm64: Remove hyp_adr/ldr_this_cpu kvm: arm64: Add helpers for accessing nVHE hyp per-cpu vars kvm: arm64: Duplicate arm64_ssbd_callback_required for nVHE hyp kvm: arm64: Create separate instances of kvm_host_data for VHE/nVHE kvm: arm64: Set up hyp percpu data for nVHE kvm: arm64: Remove unnecessary hyp mappings arch/arm64/include/asm/assembler.h | 29 +++++--- arch/arm64/include/asm/hyp_image.h | 36 ++++++++++ arch/arm64/include/asm/kvm_asm.h | 82 +++++++++++------------ arch/arm64/include/asm/kvm_host.h | 2 +- arch/arm64/include/asm/kvm_mmu.h | 22 ++---- arch/arm64/include/asm/percpu.h | 28 +++++++- arch/arm64/kernel/image-vars.h | 4 -- arch/arm64/kernel/vmlinux.lds.S | 13 ++++ arch/arm64/kvm/arm.c | 61 +++++++++++++---- arch/arm64/kvm/hyp/hyp-entry.S | 2 +- arch/arm64/kvm/hyp/include/hyp/debug-sr.h | 4 +- arch/arm64/kvm/hyp/include/hyp/switch.h | 8 +-- arch/arm64/kvm/hyp/nvhe/.gitignore | 2 + arch/arm64/kvm/hyp/nvhe/Makefile | 60 +++++++++-------- arch/arm64/kvm/hyp/nvhe/hyp.lds.S | 19 ++++++ arch/arm64/kvm/hyp/nvhe/switch.c | 8 ++- arch/arm64/kvm/hyp/vhe/switch.c | 5 +- arch/arm64/kvm/hyp/vhe/sysreg-sr.c | 4 +- arch/arm64/kvm/pmu.c | 13 ++-- 19 files changed, 272 insertions(+), 130 deletions(-) create mode 100644 arch/arm64/include/asm/hyp_image.h create mode 100644 arch/arm64/kvm/hyp/nvhe/.gitignore create mode 100644 arch/arm64/kvm/hyp/nvhe/hyp.lds.S -- 2.28.0.681.g6f77f65b4e-goog