On 26/09/2025 13:39, Daniel P. Berrangé wrote:
On Fri, Sep 26, 2025 at 01:36:25PM +0200, Markus Armbruster wrote:
Mark Cave-Ayland <mark.caveayl...@nutanix.com> writes:
Following recent discussions on the mailing list, it has been decided
that instead of mapping -cpu host and -cpu max to a suitable 32-bit x86 CPU,
it is preferable to disallow them and use the existing valid_cpu_types
validation logic so that an error is returned to the user instead.
Signed-off-by: Mark Cave-Ayland <mark.caveayl...@nutanix.com>
---
hw/i386/isapc.c | 27 ---------------------------
1 file changed, 27 deletions(-)
diff --git a/hw/i386/isapc.c b/hw/i386/isapc.c
index 44f4a44672..6c35a397df 100644
--- a/hw/i386/isapc.c
+++ b/hw/i386/isapc.c
@@ -41,31 +41,6 @@ static void pc_init_isa(MachineState *machine)
DriveInfo *hd[MAX_IDE_BUS * MAX_IDE_DEVS];
int i;
- /*
- * There is a small chance that someone unintentionally passes "-cpu max"
- * for the isapc machine, which will provide a much more modern 32-bit
- * CPU than would be expected for an ISA-era PC. If the "max" cpu type has
- * been specified, choose the "best" 32-bit cpu possible which we consider
- * be the pentium3 (deliberately choosing an Intel CPU given that the
- * default 486 CPU for the isapc machine is also an Intel CPU).
- */
- if (!strcmp(machine->cpu_type, X86_CPU_TYPE_NAME("max"))) {
- machine->cpu_type = X86_CPU_TYPE_NAME("pentium3");
- warn_report("-cpu max is invalid for isapc machine, using pentium3");
- }
-
- /*
- * Similarly if someone unintentionally passes "-cpu host" for the isapc
- * machine then display a warning and also switch to the "best" 32-bit
- * cpu possible which we consider to be the pentium3. This is because any
- * host CPU will already be modern than this, but it also ensures any
- * newer CPU flags/features are filtered out for older guests.
- */
- if (!strcmp(machine->cpu_type, X86_CPU_TYPE_NAME("host"))) {
- machine->cpu_type = X86_CPU_TYPE_NAME("pentium3");
- warn_report("-cpu host is invalid for isapc machine, using pentium3");
- }
-
if (machine->ram_size > 3.5 * GiB) {
error_report("Too much memory for this machine: %" PRId64 " MiB, "
"maximum 3584 MiB", machine->ram_size / MiB);
@@ -162,8 +137,6 @@ static void isapc_machine_options(MachineClass *m)
X86_CPU_TYPE_NAME("pentium2"),
X86_CPU_TYPE_NAME("pentium3"),
X86_CPU_TYPE_NAME("qemu32"),
- X86_CPU_TYPE_NAME("max"),
- X86_CPU_TYPE_NAME("host"),
NULL
};
PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
This reverts the "smart" part of recent
commit e1e2909f8e74051a34a044940f90d4650b6e784a
Author: Mark Cave-Ayland <mark.caveayl...@nutanix.com>
Date: Thu Aug 28 12:09:44 2025 +0100
hw/i386/pc_piix.c: restrict isapc machine to 32-bit CPUs
The isapc machine represents a legacy ISA PC with a 486 CPU. Whilst it is
possible to specify any CPU via -cpu on the command line, it makes no
sense to allow modern 64-bit CPUs to be used.
Restrict the isapc machine to the available 32-bit CPUs, taking care to
handle the case where if a user inadvertently uses either -cpu max or
-cpu host then the "best" 32-bit CPU is used (in this case the pentium3).
What is written here made sense from the POV of use of isapc with
qemu-system-x86_64, but in qemu-system-i686, both 'max' and 'host'
where already 32-bit CPUs IIUC. Both this original patch and
the new patch block them from being used in qemu-system-i686
which feels wrong given the justification above.
I tried stepping through with -cpu host/-cpu max on qemu-system-i386 and
it's a bit confusing: I think we end up with some kind of custom AMD
vendor CPU but with LM disabled. I can't easily see a way to understand
what features are currently enabled?
I must admit I'm struggling to see the usefulness of -cpu host/-cpu max
for isapc given that older OSs can be quite picky when it comes to hardware.
ATB,
Mark.
