Re: [Qemu-devel] [PATCH v2] PAM: make PAM emulation closer to documentation

[Paolo Bonzini]

On 20/07/2015 12:53, Efimov Vasily wrote:
> +    read_src = address_space_translate(read_as, pam_offset,
> +                                       &offset_within_read_leaf, &unused,
> +                                       false);
> +
> +    if (memory_region_is_ram(read_src) || memory_region_is_romd(read_src)) {
> +        /* Read source is RAM or ROM.
> +           Make current PAM region a ROM with body inside read source. */
> +        cur->ram_addr = read_src->ram_addr + offset_within_read_leaf;
> +        cur->rom_device = true;
> +        cur->romd_mode = true;
> +    } else {
> +        /* Make current PAM region a clearly I/O region. */
> +        cur->ram_addr = ~(ram_addr_t) 0;
> +        cur->rom_device = false;
> +        cur->romd_mode = false;
> +    }
> +
> +    pam->write_as = write_as;
> +    pam->read_as = read_as;
> +}
> +

Hi Vasily,

I agree that this patch is an improvement compared to the earlier
versions, but it's still a bit of an abstraction violation and I'm not
sure if it works with KVM.

Let's see if we can improve things.  Please correct me on the following:

1) For the "Make current PAM region a ROM" case, we can get the
ram_addr_t directly from the pc.bios and pc.rom MemoryRegions, and poke
into pam->region[1] and pam->region[2] when we create them.

2) For the "Make current PAM region an I/O region" case, you could add
an IOMMU region that to 0xc0000-0xfffff.  The listener would disable
pam->region[1] if address_space_translate returns an I/O region and
enable it if it returns RAM/ROM.  However, I cannot understand or
remember what is the case where you get an I/O region.

Paolo