Re: [libvirt] [Qemu-devel] Configuring pflash devices for OVMF firmware
On 31/01/19 09:33, Markus Armbruster wrote:
I thought secure=on affected only writes (and so wouldn't matter
with
readonly=on), but I was wrong:
static MemTxResult pflash_mem_read_with_attrs(void *opaque, hwaddr addr, uint64_t
*value,
unsigned len, MemTxAttrs attrs)
{
pflash_t *pfl = opaque;
bool be = !!(pfl->features & (1 << PFLASH_BE));
if ((pfl->features & (1 << PFLASH_SECURE)) && !attrs.secure)
{
*value = pflash_data_read(opaque, addr, len, be);
} else {
*value = pflash_read(opaque, addr, len, be);
}
return MEMTX_OK;
}
pflash_data_read() is what pflash_read() does when pfl->cmd is 0.
Reads from flash actually do not go through here; this function executes
if the flash chip is already in MMIO mode, which happens after you
*write* a command to the memory area. With secure=on, you just cannot
do a command write unless you're in SMM, in other words the flash chip
can only ever go in MMIO mode if you're in SMM.
Hmm, why is it okay to treat all pfl->cmd values the same when
secure=on?
But doesn't matter. You just don't want MMIO mode to be active outside
SMM: all that non-SMM code want to do with the flash is read and execute
it, as far as they're concerned it's just ROM and the command mode is
nonexistent.
Paolo