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.