Currently, the addressable ID encoding for CPUID[0x1].EBX[bits 16-23]
(Maximum number of addressable IDs for logical processors in this
physical package) is covered by vendor_cpuid_only_v2 compat property.
The previous consideration was to avoid breaking migration and this
compat property makes it unfriendly to backport the commit f985a1195b
("i386/cpu: Fix number of addressable IDs field for CPUID.01H.EBX
[23:16]").
However, NetBSD booting is broken since the commit 88dd4ca06c
("i386/cpu: Use APIC ID info to encode cache topo in CPUID[4]"),
because NetBSD calculates smt information via `lp_max` / `core_max` for
legacy Intel CPUs which doesn't support 0xb leaf, where `lp_max` is from
CPUID[0x1].EBX.bits[16-23] and `core_max` is from CPUID[0x4].0x0.bits[26
-31].
The commit 88dd4ca0 changed the encoding rule of `core_max` but didn't
update `lp_max`, so that NetBSD would get the wrong smt information,
which leads to the module loading failure.
Luckily, the commit f985a1195b ("i386/cpu: Fix number of addressable
IDs field for CPUID.01H.EBX[23:16]") updated the encoding rule for
`lp_max` and accidentally fixed the NetBSD issue too. This also shows
that using CPUID[0x1] and CPUID[0x4].0x0 to calculate HT/SMT information
is a common practice to detect CPU topology on legacy Intel CPUs.
Therefore, it's necessary to backport the commit f985a1195b to
previous stable QEMU to help address the similar issues as well. Then
the compat property is not needed any more since all stable QEMUs will
follow the same encoding way.
So, in CPUID[0x1], move addressable ID encoding out of compat property.
Reported-by: Michael Tokarev <mjt@tls.msk.ru>
Inspired-by: Chuang Xu <xuchuangxclwt@bytedance.com>
Fixes: commit f985a1195b ("i386/cpu: Fix number of addressable IDs field for CPUID.01H.EBX[23:16]")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3061
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Tested-by: Michael Tokarev <mjt@tls.msk.ru>
Message-ID: <20250804053548.1808629-1-zhao1.liu@intel.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
4e5d58969e