On Wed, Jan 04, 2023 at 04:12:34PM +0100, Laszlo Ersek wrote: > In QEMU v5.1.0, the CPU hotplug register block misbehaves: the negotiation > protocol is (effectively) broken such that it suggests that switching from > the legacy interface to the modern interface works, but in reality the > switch never happens. The symptom has been witnessed when using TCG > acceleration; KVM seems to mask the issue. The issue persists with the > following (latest) stable QEMU releases: v5.2.0, v6.2.0, v7.2.0. Currently > there is no stable release that addresses the problem. > > The QEMU bug confuses the Present and Possible counting in function > PlatformMaxCpuCountInitialization(), in > "OvmfPkg/Library/PlatformInitLib/Platform.c". OVMF ends up with Present=0 > Possible=1. This in turn further confuses MpInitLib in UefiCpuPkg (hence > firmware-time multiprocessing will be broken). Worse, CPU hot(un)plug with > SMI will be summarily broken in OvmfPkg/CpuHotplugSmm, which (considering > the privilege level of SMM) is not that great. > > Detect the issue in PlatformMaxCpuCountInitialization(), and print an > error message and *hang* if the issue is present. > > The problem was originally reported by Ard [0]. We analyzed it at [1] and > [2]. A QEMU patch was sent at [3]. > > [0] https://bugzilla.tianocore.org/show_bug.cgi?id=4234#c2 > > [1] https://bugzilla.tianocore.org/show_bug.cgi?id=4234#c3 > > [2] IO port write width clamping differs between TCG and KVM > > http://mid.mail-archive.com/aaedee84-d3ed-a4f9-21e7-d221a28d1683@redhat.com > https://lists.gnu.org/archive/html/qemu-devel/2023-01/msg00199.html > > [3] acpi: cpuhp: fix guest-visible maximum access size to the legacy reg block > http://mid.mail-archive.com/20230104090138.214862-1-lersek@redhat.com > https://lists.gnu.org/archive/html/qemu-devel/2023-01/msg00278.html > > NOTE: PlatformInitLib is used in the following platform DSCs: > > OvmfPkg/AmdSev/AmdSevX64.dsc > OvmfPkg/CloudHv/CloudHvX64.dsc > OvmfPkg/IntelTdx/IntelTdxX64.dsc > OvmfPkg/Microvm/MicrovmX64.dsc > OvmfPkg/OvmfPkgIa32.dsc > OvmfPkg/OvmfPkgIa32X64.dsc > OvmfPkg/OvmfPkgX64.dsc > > but I can only test this change with the last three platforms, running on > QEMU. > > Test results: > > TCG QEMU OVMF result > patched patched > --- ------- ------- ------------------------------------------------- > 0 0 0 CPU counts OK (KVM masks the QEMU bug) > 0 0 1 CPU counts OK (KVM masks the QEMU bug) > 0 1 0 CPU counts OK (QEMU fix, but KVM masks the QEMU > bug anyway) > 0 1 1 CPU counts OK (QEMU fix, but KVM masks the QEMU > bug anyway) > 1 0 0 boot with broken CPU counts (original QEMU bug) > 1 0 1 broken CPU count caught (boot hangs) > 1 1 0 CPU counts OK (QEMU fix) > 1 1 1 CPU counts OK (QEMU fix) > > Cc: Ard Biesheuvel <ardb+tianoc...@kernel.org> > Cc: Brijesh Singh <brijesh.si...@amd.com> > Cc: Erdem Aktas <erdemak...@google.com> > Cc: Gerd Hoffmann <kra...@redhat.com> > Cc: James Bottomley <j...@linux.ibm.com> > Cc: Jiewen Yao <jiewen....@intel.com> > Cc: Jordan Justen <jordan.l.jus...@intel.com> > Cc: Min Xu <min.m...@intel.com> > Cc: Sebastien Boeuf <sebastien.bo...@intel.com> > Cc: Tom Lendacky <thomas.lenda...@amd.com> > Bugzilla: https://bugzilla.tianocore.org/show_bug.cgi?id=4250 > Signed-off-by: Laszlo Ersek <ler...@redhat.com>
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