On 8/27/2025 7:10 PM, Mark Cave-Ayland wrote:
On 26/08/2025 08:25, Xiaoyao Li wrote:
On 8/22/2025 8:11 PM, Mark Cave-Ayland wrote:
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 -cpu max then the
"best"
32-bit CPU is used (in this case the pentium3).
Signed-off-by: Mark Cave-Ayland <mark.caveayl...@nutanix.com>
Reviewed-by: Philippe Mathieu-Daudé <phi...@linaro.org>
---
hw/i386/pc_piix.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index c03324281b..5720b6b556 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -436,6 +436,19 @@ static void pc_set_south_bridge(Object *obj, int
value, Error **errp)
#ifdef CONFIG_ISAPC
static void pc_init_isa(MachineState *machine)
{
+ /*
+ * 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");
+ }
Do we need to handle the case of "-cpu host"?
I don't believe so. I wasn't originally planning to support "-cpu max"
for isapc, however Daniel mentioned that it could possibly be generated
from libvirt so it makes sense to add the above check to warn in this
case and then continue.
"host" cpu type is the child of "max", so "-cpu host" will pass in the
is_cpu_type_supported(), the same as "max".
While we are changing "max" to "pentium3", I think it needs to do the
same for "host". Otherwise, "-cpu host" won't get any warning and expose
the native features to the VMs that are mostly not supposed to exist for
isapc, e.g., the LM CUPID bit.
