Date: Sat, 28 Mar 2026 05:56:28 +0000 From: Colin Percival <cperciva@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: d9db6d759dfc - main - x86: Add stub for Extended Destination ID support Message-ID: <69c76d8c.3e2c5.628c6a14@gitrepo.freebsd.org>
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The branch main has been updated by cperciva: URL: https://cgit.FreeBSD.org/src/commit/?id=d9db6d759dfcf4a4559e66e777599bb3fa8ca14c commit d9db6d759dfcf4a4559e66e777599bb3fa8ca14c Author: Colin Percival <cperciva@FreeBSD.org> AuthorDate: 2026-03-16 23:37:04 +0000 Commit: Colin Percival <cperciva@FreeBSD.org> CommitDate: 2026-03-28 05:54:00 +0000 x86: Add stub for Extended Destination ID support Without an IOMMU, the APIC standard only allows 8 bits of Destination ID for MSI messages, limiting us to 256 CPUs. While IOMMUs can allow for more than 256 CPUs to be supported, they are not necessarily desirable in virtualized environments. The Extended Destination ID standard authored by David Woodhouse uses 7 "Reserved" bits for the high bits of a 15-bit Extended Destination ID in order to address this: http://david.woodhou.se/ExtDestId.pdf Add a loader tunable machdep.apic_ext_dest_id to control the use of this feature; the default value (-1) means "autodetect" while 0 and 1 mean disabled and enabled respectively. Code to detect host support in Xen, Hyper-V, KVM, and Bhyve will come in future commits, as will the code to use this setting in msi_map and ioapic_program_intpin. Tested on: EC2 r8i.96xlarge MFC after: 3 weeks Sponsored by: Amazon Differential Revision: https://reviews.freebsd.org/D55890 --- sys/x86/include/apicvar.h | 1 + sys/x86/x86/local_apic.c | 15 +++++++++++++++ 2 files changed, 16 insertions(+) diff --git a/sys/x86/include/apicvar.h b/sys/x86/include/apicvar.h index 551f5527ac00..c2f4414ec8db 100644 --- a/sys/x86/include/apicvar.h +++ b/sys/x86/include/apicvar.h @@ -265,6 +265,7 @@ device_t ioapic_get_dev(u_int apic_id); extern int x2apic_mode; extern int lapic_eoi_suppression; +extern int apic_ext_dest_id; #ifdef _SYS_SYSCTL_H_ SYSCTL_DECL(_hw_apic); diff --git a/sys/x86/x86/local_apic.c b/sys/x86/x86/local_apic.c index 888fd266d364..21934b41ea62 100644 --- a/sys/x86/x86/local_apic.c +++ b/sys/x86/x86/local_apic.c @@ -2086,6 +2086,17 @@ apic_setup_local(void *dummy __unused) } SYSINIT(apic_setup_local, SI_SUB_CPU, SI_ORDER_SECOND, apic_setup_local, NULL); +/* Are we in a VM which supports the Extended Destination ID standard? */ +int apic_ext_dest_id = -1; +SYSCTL_INT(_machdep, OID_AUTO, apic_ext_dest_id, CTLFLAG_RDTUN, &apic_ext_dest_id, 0, + "Use APIC Extended Destination IDs"); + +/* Detect support for Extended Destination IDs. */ +static void +detect_extended_dest_id(void) +{ +} + /* * Setup the I/O APICs. */ @@ -2097,6 +2108,10 @@ apic_setup_io(void *dummy __unused) if (best_enum == NULL) return; + /* Check hypervisor support for extended destination IDs. */ + if (apic_ext_dest_id == -1) + detect_extended_dest_id(); + /* * Local APIC must be registered before other PICs and pseudo PICs * for proper suspend/resume order.home | help
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