On Mon, Mar 06, 2023 at 09:46:55AM +0100, Thomas Huth wrote:
Aside from not supporting KVM on 32-bit hosts, the qemu-system-x86_64 binary is a proper superset of the qemu-system-i386 binary. With the 32-bit host support being deprecated, it is now also possible to deprecate the qemu-system-i386 binary.
With regards to 32-bit KVM support in the x86 Linux kernel, the developers confirmed that they do not need a recent qemu-system-i386 binary here:
https://lore.kernel.org/kvm/Y%2ffkTs5ajFy0hP1U@google.com/
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> Reviewed-by: Wilfred Mallawa <wilfred.mallawa@wdc.com> Signed-off-by: Thomas Huth <thuth@redhat.com> --- docs/about/deprecated.rst | 14 ++++++++++++++ 1 file changed, 14 insertions(+)
diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst index 1ca9dc33d6..c4fcc6b33c 100644 --- a/docs/about/deprecated.rst +++ b/docs/about/deprecated.rst @@ -34,6 +34,20 @@ deprecating the build option and no longer defend it in CI. The ``--enable-gcov`` build option remains for analysis test case coverage.
+``qemu-system-i386`` binary (since 8.0) +''''''''''''''''''''''''''''''''''''''' + +The ``qemu-system-i386`` binary was mainly useful for running with KVM +on 32-bit x86 hosts, but most Linux distributions already removed their +support for 32-bit x86 kernels, so hardly anybody still needs this. The +``qemu-system-x86_64`` binary is a proper superset and can be used to +run 32-bit guests by selecting a 32-bit CPU model, including KVM support +on x86_64 hosts. Thus users are recommended to reconfigure their systems +to use the ``qemu-system-x86_64`` binary instead. If a 32-bit CPU guest +environment should be enforced, you can switch off the "long mode" CPU +flag, e.g. with ``-cpu max,lm=off``.
I had the idea to check this today and this is not quite sufficient, because we have code that changes the family/model/stepping for 'max' which is target dependent: #ifdef TARGET_X86_64 object_property_set_int(OBJECT(cpu), "family", 15, &error_abort); object_property_set_int(OBJECT(cpu), "model", 107, &error_abort); object_property_set_int(OBJECT(cpu), "stepping", 1, &error_abort); #else object_property_set_int(OBJECT(cpu), "family", 6, &error_abort); object_property_set_int(OBJECT(cpu), "model", 6, &error_abort); object_property_set_int(OBJECT(cpu), "stepping", 3, &error_abort); #endif The former is a 64-bit AMD model and the latter is a 32-bit model. Seems LLVM was sensitive to this distinction to some extent: https://gitlab.com/qemu-project/qemu/-/issues/191 A further difference is that qemy-system-i686 does not appear to enable the 'syscall' flag, but I've not figured out where that difference is coming from in the code. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|