[Qemu-devel] subpages with memory region aliases (was: [PATCH 3/6] kvmvapic: Introduce TPR access optimization for Windows guests)

[Jan Kiszka <jan.kiszka@web.de>]

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Avi,

Before I forget:

On 2012-02-05 13:39, Jan Kiszka wrote:
> +static void vapic_map_rom_writable(VAPICROMState *s)
> +{
> +    target_phys_addr_t rom_paddr = s->rom_state_paddr & ROM_BLOCK_MASK;
> +    MemoryRegionSection section;
> +    MemoryRegion *as;
> +    size_t rom_size;
> +    uint8_t *ram;
> +
> +    as = sysbus_address_space(&s->busdev);
> +
> +    if (s->rom_mapped_writable) {
> +        memory_region_del_subregion(as, &s->rom);
> +        memory_region_destroy(&s->rom);
> +    }
> +
> +    /* grab RAM memory region (region @rom_paddr may still be pc.rom) */
> +    section = memory_region_find(as, 0, 1);
> +
> +    /* read ROM size from RAM region */
> +    ram = memory_region_get_ram_ptr(section.mr);
> +    rom_size = ram[rom_paddr + 2] * ROM_BLOCK_SIZE;
> +    s->rom_size = rom_size;
> +
> +    /* FIXME: round up as everything underneath would fall apart otherwise
> +     * (subpages are broken) */
> +    rom_size = TARGET_PAGE_ALIGN(rom_size);

Removing this alignment triggers an interesting bug in the memory layer.
Haven't understood the details yet. Is subpage support supposed to work?

> +
> +    memory_region_init_alias(&s->rom, "kvmvapic-rom", section.mr, rom_paddr,
> +                             rom_size);
> +    memory_region_add_subregion_overlap(as, rom_paddr, &s->rom, 1000);
> +    s->rom_mapped_writable = true;
> +}

Jan



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