On 11/7/25 11:57, Mark Cave-Ayland wrote:
All isapc machines must have 32-bit CPUs and so the RAM split logic can be
hardcoded
accordingly.
Signed-off-by: Mark Cave-Ayland <mark.caveayl...@nutanix.com>
---
hw/i386/pc_piix.c | 58 ++++-------------------------------------------
1 file changed, 4 insertions(+), 54 deletions(-)
diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index 78f50a7893..fbd9500061 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -426,69 +426,19 @@ static void pc_init_isa(MachineState *machine)
GSIState *gsi_state;
MemoryRegion *ram_memory;
MemoryRegion *rom_memory = system_memory;
- ram_addr_t lowmem;
uint64_t hole64_size = 0;
/*
- * Calculate ram split, for memory below and above 4G. It's a bit
- * complicated for backward compatibility reasons ...
- *
- * - Traditional split is 3.5G (lowmem = 0xe0000000). This is the
- * default value for max_ram_below_4g now.
- *
- * - Then, to gigabyte align the memory, we move the split to 3G
- * (lowmem = 0xc0000000). But only in case we have to split in
- * the first place, i.e. ram_size is larger than (traditional)
- * lowmem. And for new machine types (gigabyte_align = true)
- * only, for live migration compatibility reasons.
- *
- * - Next the max-ram-below-4g option was added, which allowed to
- * reduce lowmem to a smaller value, to allow a larger PCI I/O
- * window below 4G. qemu doesn't enforce gigabyte alignment here,
- * but prints a warning.
- *
- * - Finally max-ram-below-4g got updated to also allow raising lowmem,
- * so legacy non-PAE guests can get as much memory as possible in
- * the 32bit address space below 4G.
- *
- * - Note that Xen has its own ram setup code in xen_ram_init(),
- * called via xen_hvm_init_pc().
- *
- * Examples:
- * qemu -M pc-1.7 -m 4G (old default) -> 3584M low, 512M high
- * qemu -M pc -m 4G (new default) -> 3072M low, 1024M high
- * qemu -M pc,max-ram-below-4g=2G -m 4G -> 2048M low, 2048M high
- * qemu -M pc,max-ram-below-4g=4G -m 3968M -> 3968M low (=4G-128M)
+ * There is no RAM split for the isapc machine
*/
if (xen_enabled()) {
xen_hvm_init_pc(pcms, &ram_memory);
} else {
ram_memory = machine->ram;
- if (!pcms->max_ram_below_4g) {
- pcms->max_ram_below_4g = 0xe0000000; /* default: 3.5G */
- }
- lowmem = pcms->max_ram_below_4g;
- if (machine->ram_size >= pcms->max_ram_below_4g) {
- if (pcmc->gigabyte_align) {
- if (lowmem > 0xc0000000) {
- lowmem = 0xc0000000;
- }
- if (lowmem & (1 * GiB - 1)) {
- warn_report("Large machine and max_ram_below_4g "
- "(%" PRIu64 ") not a multiple of 1G; "
- "possible bad performance.",
- pcms->max_ram_below_4g);
- }
- }
- }
- if (machine->ram_size >= lowmem) {
- x86ms->above_4g_mem_size = machine->ram_size - lowmem;
- x86ms->below_4g_mem_size = lowmem;
- } else {
- x86ms->above_4g_mem_size = 0;
- x86ms->below_4g_mem_size = machine->ram_size;
- }
+ pcms->max_ram_below_4g = 0xe0000000; /* default: 3.5G */
Since nothing to split, I'd expect the whole 4*GiB space here.
+ x86ms->above_4g_mem_size = 0;
+ x86ms->below_4g_mem_size = machine->ram_size;
}
/*
