In certain code paths, KVM/ARM currently invalidates the entire VM's page-tables instead of just invalidating a necessary range. For example, when collapsing a table PTE to a block PTE, instead of iterating over each PTE and flushing them, KVM uses 'vmalls12e1is' TLBI operation to flush all the entries. This is inefficient since the guest would have to refill the TLBs again, even for the addresses that aren't covered by the table entry. The performance impact would scale poorly if many addresses in the VM is going through this remapping. For architectures that implement FEAT_TLBIRANGE, KVM can replace such inefficient paths by performing the invalidations only on the range of addresses that are in scope. This series tries to achieve the same in the areas of stage-2 map, unmap and write-protecting the pages. Patch-1 refactors the core arm64's __flush_tlb_range() to be used by other entities. Patch-2 adds a range-based TLBI mechanism for KVM (VHE and nVHE). Patch-3 implements the kvm_arch_flush_remote_tlbs_range() for arm64. Patch-4 aims to flush only the memslot that undergoes a write-protect, instead of the entire VM. Patch-5 operates on stage2_try_break_pte() to use the range based TLBI instructions when collapsing a table entry. The map path is the immediate consumer of this when KVM remaps a table entry into a block. Patch-6 Adds a 'skip_flush' parameter to stage2_put_pte() for the next patch to take advantage of during TLB invalidations in unmap path. Patch-7 modifies the stage-2 unmap path in which, if the system supports FEAT_TLBIRANGE, the TLB invalidations are skipped during the page-table. walk. Instead it's done in one go after the entire walk is finished. The series is based off of upstream v6.3-rc5, and applied David Matlack's common API for TLB invalidations[1] on top. The performance evaluation was done on a hardware that supports FEAT_TLBIRANGE, on a VHE configuration, using a modified kvm_page_table_test. The modified version updates the guest code in the ADJUST_MAPPINGS case to not only access this page but also to access up to 512 pages backwards for every new page it iterates through. This is done to test the effect of TLBI misses after KVM has handled a fault. The series captures the impact in the map and unmap paths as described above. $ kvm_page_table_test -m 2 -v 128 -s anonymous_hugetlb_2mb -b $i +--------+------------------------------+------------------------------+ | mem_sz | ADJUST_MAPPINGS (s) | Unmap VM (s) | | (GB) | Baseline | Baseline + series | Baseline | Baseline + series | +--------+----------|-------------------+------------------------------+ | 1 | 5.25 | 5.42 | 0.007 | 0.005 | | 2 | 9.40 | 7.23 | 0.010 | 0.006 | | 4 | 20.96 | 13.09 | 0.015 | 0.008 | | 8 | 41.32 | 26.06 | 0.025 | 0.012 | | 16 | 76.00 | 53.40 | 0.045 | 0.017 | | 32 | 85.92 | 82.87 | 0.077 | 0.028 | | 64 | 178.99 | 168.45 | 0.142 | 0.049 | | 128 | 359.76 | 316.66 | 0.280 | 0.082 | +--------+----------+-------------------+----------+-------------------+ $ kvm_page_table_test -m 2 -b 128G -s anonymous_hugetlb_2mb -v $i +--------+------------------------------+ | vCPUs | ADJUST_MAPPINGS (s) | | | Baseline | Baseline + series | +--------+----------|-------------------+ | 1 | 130.84 | 139.65 | | 2 | 91.42 | 105.49 | | 4 | 98.83 | 97.68 | | 8 | 108.28 | 104.90 | | 16 | 110.69 | 108.28 | | 32 | 146.47 | 120.02 | | 64 | 204.04 | 185.88 | | 128 | 359.76 | 316.66 | +--------+----------+-------------------+ For the ADJUST_MAPPINGS cases, which maps back the 4K table entries to 2M hugepages, the series sees an average improvement of ~15%. For unmapping 2M hugepages, we see at least a 3x improvement. $ kvm_page_table_test -m 2 -b $i +--------+------------------------------+ | mem_sz | Unmap VM (s) | | (GB) | Baseline | Baseline + series | +--------+------------------------------+ | 1 | 1.03 | 0.58 | | 2 | 1.57 | 0.72 | | 4 | 2.65 | 0.98 | | 8 | 4.77 | 1.54 | | 16 | 9.06 | 2.57 | | 32 | 17.60 | 4.41 | | 64 | 34.72 | 8.92 | | 128 | 68.92 | 17.70 | +--------+----------+-------------------+ The series sees an average gain of 4x when the guest backed by PAGE_SIZE (4K) pages. v3: Thanks, Oliver for all the suggestions. - The core flush API (__kvm_tlb_flush_vmid_range()) now checks if the system support FEAT_TLBIRANGE or not, thus elimiating the redundancy in the upper layers. - If FEAT_TLBIRANGE is not supported, the implementation falls back to invalidating all the TLB entries with the VMID, instead of doing an iterative flush for the range. - The kvm_arch_flush_remote_tlbs_range() doesn't return -EOPNOTSUPP if the system doesn't implement FEAT_TLBIRANGE. It depends on __kvm_tlb_flush_vmid_range() to do take care of the decisions and return 0 regardless of the underlying feature support. - __kvm_tlb_flush_vmid_range() doesn't take 'level' as input to calculate the 'stride'. Instead, it always assumes PAGE_SIZE. - Fast unmap path is eliminated. Instead, the existing unmap walker is modified to skip the TLBIs during the walk, and do it all at once after the walk, using the range-based instructions. v2: https://lore.kernel.org/all/20230206172340.2639971-1-rananta@xxxxxxxxxx/ - Rebased the series on top of David Matlack's series for common TLB invalidation API[1]. - Implement kvm_arch_flush_remote_tlbs_range() for arm64, by extending the support introduced by [1]. - Use kvm_flush_remote_tlbs_memslot() introduced by [1] to flush only the current memslot after write-protect. - Modified the __kvm_tlb_flush_range() macro to accepts 'level' as an argument to calculate the 'stride' instead of just using PAGE_SIZE. - Split the patch that introduces the range-based TLBI to KVM and the implementation of IPA-based invalidation into its own patches. - Dropped the patch that tries to optimize the mmu notifiers paths. - Rename the function kvm_table_pte_flush() to kvm_pgtable_stage2_flush_range(), and accept the range of addresses to flush. [Oliver] - Drop the 'tlb_level' argument for stage2_try_break_pte() and directly pass '0' as 'tlb_level' to kvm_pgtable_stage2_flush_range(). [Oliver] v1: https://lore.kernel.org/all/20230109215347.3119271-1-rananta@xxxxxxxxxx/ Thank you. Raghavendra [1]: https://lore.kernel.org/linux-arm-kernel/20230126184025.2294823-1-dmatlack@xxxxxxxxxx/ Raghavendra Rao Ananta (7): arm64: tlb: Refactor the core flush algorithm of __flush_tlb_range KVM: arm64: Implement __kvm_tlb_flush_vmid_range() KVM: arm64: Implement kvm_arch_flush_remote_tlbs_range() KVM: arm64: Flush only the memslot after write-protect KVM: arm64: Invalidate the table entries upon a range KVM: arm64: Add 'skip_flush' arg to stage2_put_pte() KVM: arm64: Use TLBI range-based intructions for unmap arch/arm64/include/asm/kvm_asm.h | 3 + arch/arm64/include/asm/kvm_host.h | 3 + arch/arm64/include/asm/tlbflush.h | 108 +++++++++++++++-------------- arch/arm64/kvm/hyp/nvhe/hyp-main.c | 11 +++ arch/arm64/kvm/hyp/nvhe/tlb.c | 39 +++++++++++ arch/arm64/kvm/hyp/pgtable.c | 49 ++++++++++--- arch/arm64/kvm/hyp/vhe/tlb.c | 35 ++++++++++ arch/arm64/kvm/mmu.c | 13 +++- 8 files changed, 198 insertions(+), 63 deletions(-) -- 2.40.0.634.g4ca3ef3211-goog
