Date: Wed, 22 Mar 2023 13:19:36 GMT From: Mark Johnston <markj@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: ef0ac973dbc8 - main - bhyve: Sleep briefly in the VMEXIT_DEBUG handler Message-ID: <202303221319.32MDJal8097063@gitrepo.freebsd.org>
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The branch main has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=ef0ac973dbc8c54214ac8c61891abd832cd5b700 commit ef0ac973dbc8c54214ac8c61891abd832cd5b700 Author: Mark Johnston <markj@FreeBSD.org> AuthorDate: 2023-03-22 13:02:54 +0000 Commit: Mark Johnston <markj@FreeBSD.org> CommitDate: 2023-03-22 13:19:27 +0000 bhyve: Sleep briefly in the VMEXIT_DEBUG handler As of commit 0bda8d3e9f7a ("vmm: permit some IPIs to be handled by userspace") and commit 9cc9abf409cc ("bhyve: create all vcpus on startup"), we have a misbehaviour where AP vCPU threads spin until they receive a SIPI. In particular, since they are "suspended", they simply call the VMEXIT_DEBUG handler in a loop, but the handler is a no-op by default. This is tricky to fix since the gdb stub isn't aware of whether a given vCPU is supposed to be running. For 13.2's sake, introduce a simple workaround wherein the VMEXIT_DEBUG handler sleeps for a short period. This ensures that host CPU usage remains sane when VMs are starting without penalizing users of VMEXIT_DEBUG too much. Reviewed by: corvink, jhb MFC after: 3 days Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D39174 --- usr.sbin/bhyve/bhyverun.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/usr.sbin/bhyve/bhyverun.c b/usr.sbin/bhyve/bhyverun.c index 665fec73e48c..dd30eb4405ef 100644 --- a/usr.sbin/bhyve/bhyverun.c +++ b/usr.sbin/bhyve/bhyverun.c @@ -911,6 +911,11 @@ vmexit_debug(struct vmctx *ctx __unused, struct vm_exit *vme __unused, #ifdef BHYVE_SNAPSHOT checkpoint_cpu_resume(*pvcpu); #endif + /* + * XXX-MJ sleep for a short period to avoid chewing up the CPU in the + * window between activation of the vCPU thread and the STARTUP IPI. + */ + usleep(1000); return (VMEXIT_CONTINUE); }
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