On Tue, May 20, 2014 at 02:22:16PM +0100, David Woodhouse wrote:
Unless CONFIG_MALLOC_UPPERMEMORY is turned off, we expect to use the space between the top of option ROMs and the bottom of our own BIOS code as a stack. OVMF was previously marking the whole region from 0xC0000 to 0xFFFFF read-only before invoking our Legacy16Boot method. Read-only stack considered harmful.
Version 0.98 of the CSM spec adds the UmaAddress and UmaSize fields, which allow the CSM to specify a memory region that needs to be writable, so provide that information.
[...]
--- a/src/fw/csm.c +++ b/src/fw/csm.c @@ -34,6 +34,10 @@ EFI_COMPATIBILITY16_TABLE csm_compat_table VARFSEG __aligned(16) = { .Compatibility16CallOffset = 0 /* Filled in by checkrom.py */, .OemIdStringPointer = (u32)"SeaBIOS", .AcpiRsdPtrPointer = (u32)&csm_rsdp, +#if CONFIG_MALLOC_UPPERMEMORY
- .UmaAddress = (u32)&zonelow_base,
- .UmaSize = 0x10000,
+#endif
Is there an advantage to setting this at compile time vs only setting these fields during runtime?
@@ -49,6 +53,11 @@ csm_return(struct bregs *regs) dprintf(3, "handle_csm returning AX=%04x\n", regs->ax);
PICMask = pic_irqmask_read();
- if (CONFIG_MALLOC_UPPERMEMORY) {
u32 top = rom_get_max();csm_compat_table.UmaAddress = top;csm_compat_table.UmaSize = (u32)zonelow_base + 0x10000 - top;- }
Would this work instead?
u32 rommax = rom_get_max(); extern u8 final_readonly_start[]; csm_compat_table.UmaAddress = rommax; csm_compat_table.UmaSize = (u32)final_readonly_start - rommax;
This should result in the same values as your patch when CONFIG_MALLOC_UPPERMEMORY. For !CONFIG_MALLOC_UPPERMEMORY it will result in UmaAddress==final_readonly_start and UmaSize==0.
-Kevin