[PW_SID:1162101] RISC-V: KVM: Avoid synchronous IPIs on VMID rollover - #2637
Closed
linux-riscv-bot wants to merge 1 commit into
Closed
[PW_SID:1162101] RISC-V: KVM: Avoid synchronous IPIs on VMID rollover#2637linux-riscv-bot wants to merge 1 commit into
linux-riscv-bot wants to merge 1 commit into
Conversation
The current VMID rollover path synchronously invokes HFENCE.GVMA on all online CPUs using on_each_cpu_mask(). This sends IPIs to remote CPUs and causes a vCPU running in guest mode on a targeted CPU to exit. The rollover path then waits for all CPUs to complete their local TLB flushes before VMID allocation can continue. Make VMID rollover lazy to remove this cross-CPU synchronization. Track active and reserved software VMIDs for each possible CPU. On rollover, preserve hardware VMIDs that may still have stale translations, clear the active VMID, and mark a local TLB flush pending for each CPU. Do not send IPIs or otherwise force remote vCPUs to exit during rollover. Instead, when a CPU next activates a VMID before guest entry, perform the pending local HFENCE.GVMA and only then publish the new active VMID. Perform VMID activation after preemption is disabled in the guest entry path. This keeps the per-CPU active VMID and pending flush state associated with the same CPU that subsequently enters guest mode. Keep reserved hardware VMIDs unavailable to the bitmap allocator while stale translations associated with them may still exist. This prevents a hardware VMID from being reused prematurely after a generation rollover. Represent a software VMID as a generation combined with a hardware VMID, and extract only the hardware VMID when programming HGATP or issuing VMID-specific fences. Reserve hardware VMID 0. Disable VMID allocation when the hardware VMID space is too small to retain one reserved VMID per possible CPU while still leaving a VMID available for a new allocation. Invalidate the per-CPU VMID bookkeeping when virtualization is disabled, so stale G-stage translations are flushed before the CPU next enters a guest. This removes IPIs and remote CPU synchronization from the VMID rollover path, avoiding VM exits caused solely by VMID exhaustion on another CPU. Tested on QEMU with two host CPUs and the VMID width temporarily forced to 2 bits. Repeated rollover, protection against premature VMID reuse, activation-versus-rollover stress, and vCPU migration were exercised with multiple concurrent guests without guest failures or host warnings. Assisted-by: YuanSheng:deepseek-v4-pro Co-developed-by: Quan Zhou <zhouquan@iscas.ac.cn> Signed-off-by: Quan Zhou <zhouquan@iscas.ac.cn> Signed-off-by: Wenlong Li <wenlongli486@gmail.com> Signed-off-by: Linux RISC-V bot <linux.riscv.bot@gmail.com>
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
PR for series 1162101 applied to workflow__riscv__fixes
Name: RISC-V: KVM: Avoid synchronous IPIs on VMID rollover
URL: https://patchwork.kernel.org/series/1162101/
Version: 1