Re: [Qemu-devel] [PATCH v2] hw/i386/pc_sysfw: support two flash drives

[Markus Armbruster]

Laszlo Ersek <address@hidden> writes:

> This patch allows the user to usefully specify
>
>   -drive file=img_1,if=pflash,format=raw,readonly \
>   -drive file=img_2,if=pflash,format=raw
>
> on the command line. The flash images will be mapped under 4G in their
> reverse unit order -- that is, with their base addresses progressing
> downwards, in increasing unit order.
>
> (The unit number increases with command line order if not explicitly
> specified.)
>
> This accommodates the following use case: suppose that OVMF is split in
> two parts, a writeable host file for non-volatile variable storage, and a
> read-only part for bootstrap and decompressible executable code.
>
> The binary code part would be read-only, centrally managed on the host
> system, and passed in as unit 0. The variable store would be writeable,
> VM-specific, and passed in as unit 1.
>
>   00000000ffe00000-00000000ffe1ffff (prio 0, R-): system.flash1
>   00000000ffe20000-00000000ffffffff (prio 0, R-): system.flash0
>
> (If the guest tries to write to the flash range that is backed by the
> read-only drive, pflash_update() is never called; various flash
> programming/erase errors are returned to the guest instead. See the
> callers of pflash_update(), and the initialization of "pfl->ro", in
> "hw/block/pflash_cfi01.c".)
>
> Signed-off-by: Laszlo Ersek <address@hidden>
> ---
>  v2:
>  - don't map flash devices beyond unit#1 [Markus]
>  - explicit low bound on cumulative base address [Markus]
>  - updated comment block on pc_system_flash_init() [Laszlo]
>  - dropped (DriveInfo*) param of pc_system_flash_init(), use drive_get()
>    internally for unit#0 too [Markus]
>  - turn do-loop into for-loop [Markus]
>  - check bdrv_getlength() for errors [Laszlo]
>  - reject zero-sized flash [Laszlo]
>  - use Location of -pflash / -drive if=pflash,... option in error
>    reporting [Markus]
>  - describe the real spots where write attempts to r/o flash are caught
>    [Laszlo]
>
>  hw/i386/pc_sysfw.c | 105 
> +++++++++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 86 insertions(+), 19 deletions(-)
>
> diff --git a/hw/i386/pc_sysfw.c b/hw/i386/pc_sysfw.c
> index e917c83..75a7ebb 100644
> --- a/hw/i386/pc_sysfw.c
> +++ b/hw/i386/pc_sysfw.c
> @@ -72,35 +72,102 @@ static void pc_isa_bios_init(MemoryRegion *rom_memory,
>      memory_region_set_readonly(isa_bios, true);
>  }
>  
> -static void pc_system_flash_init(MemoryRegion *rom_memory,
> -                                 DriveInfo *pflash_drv)
> +#define FLASH_MAP_UNIT_MAX 2
> +
> +/* We don't have a theoretically justifiable exact lower bound on the base
> + * address of any flash mapping. In practice, the IO-APIC MMIO range is
> + * [0xFEE00000..0xFEE01000[ -- see IO_APIC_DEFAULT_ADDRESS --, leaving free
> + * only 18MB-4KB below 4G. For now, restrict the cumulative mapping to 8MB in
> + * size.
> + */
> +#define FLASH_MAP_BASE_MIN ((hwaddr)(0x100000000ULL - 8*1024*1024))
> +
> +/* This function maps flash drives from 4G downward, in order of their unit
> + * numbers. The mapping starts at unit#0, with unit number increments of 1, 
> and
> + * stops before the first missing flash drive, or before
> + * unit#FLASH_MAP_UNIT_MAX, whichever is reached first.
> + *
> + * Addressing within one flash drive is of course not reversed.
> + *
> + * An error message is printed and the process exits if:
> + * - the size of the backing file for a flash drive is non-positive, or not a
> + *   multiple of the required sector size, or
> + * - the current mapping's base address would fall below FLASH_MAP_BASE_MIN.
> + *
> + * The drive with unit#0 (if available) is mapped at the highest address, and
> + * it is passed to pc_isa_bios_init(). Merging several drives for isa-bios is
> + * not supported.
> + */
> +static void pc_system_flash_init(MemoryRegion *rom_memory)
>  {
> +    int unit;
> +    DriveInfo *pflash_drv;
>      BlockDriverState *bdrv;
>      int64_t size;
> -    hwaddr phys_addr;
> +    char *fatal_errmsg = NULL;
> +    hwaddr phys_addr = 0x100000000ULL;
>      int sector_bits, sector_size;
>      pflash_t *system_flash;
>      MemoryRegion *flash_mem;
> +    char name[64];
>  
> -    bdrv = pflash_drv->bdrv;
> -    size = bdrv_getlength(pflash_drv->bdrv);
>      sector_bits = 12;
>      sector_size = 1 << sector_bits;
>  
> -    if ((size % sector_size) != 0) {
> -        fprintf(stderr,
> -                "qemu: PC system firmware (pflash) must be a multiple of 
> 0x%x\n",
> -                sector_size);
> -        exit(1);
> +    for (unit = 0;
> +         (unit < FLASH_MAP_UNIT_MAX &&
> +          (pflash_drv = drive_get(IF_PFLASH, 0, unit)) != NULL);
> +         ++unit) {
> +        bdrv = pflash_drv->bdrv;

Used just twice, sure it's worth a variable?  Your choice, of course.

> +        size = bdrv_getlength(bdrv);
> +        if (size < 0) {
> +            fatal_errmsg = g_strdup_printf("failed to get backing file 
> size");
> +        } else if (size == 0) {
> +            fatal_errmsg = g_strdup_printf("PC system firmware (pflash) "
> +                               "cannot have zero size");
> +        } else if ((size % sector_size) != 0) {
> +            fatal_errmsg = g_strdup_printf("PC system firmware (pflash) "
> +                               "must be a multiple of 0x%x", sector_size);
> +        } else if (phys_addr < size || phys_addr - size < 
> FLASH_MAP_BASE_MIN) {
> +            fatal_errmsg = g_strdup_printf("oversized backing file, pflash "
> +                               "segments cannot be mapped under "

"mapped below "?

> +                               TARGET_FMT_plx, FLASH_MAP_BASE_MIN);
> +        }
> +        if (fatal_errmsg != NULL) {
> +            Location loc;
> +
> +            /* push a new, "none" location on the location stack; overwrite 
> its
> +             * contents with the location saved in the option; print the 
> error
> +             * (includes location); pop the top
> +             */

Sure this comment is worthwhile?  Your decision.

I suspect we should have error_report_loc().

> +            loc_push_none(&loc);
> +            if (pflash_drv->opts != NULL) {
> +                qemu_opts_loc_restore(pflash_drv->opts);
> +            }
> +            error_report("%s", fatal_errmsg);
> +            loc_pop(&loc);
> +            g_free(fatal_errmsg);
> +            exit(1);

You hoist the reporting of a fatal error out of the conditionals.  If we
had error_report_loc(), we could leave it there.  But we don't.

> +        }
> +
> +        phys_addr -= size;
> +
> +        /* pflash_cfi01_register() creates a deep copy of the name */
> +        snprintf(name, sizeof name, "system.flash%d", unit);
> +        system_flash = pflash_cfi01_register(phys_addr, NULL /* qdev */, 
> name,

pflash_cfi01_register() doesn't use its second parameter, and all
callers pass NULL, ugh.

I looked because I don't like nor trust /* name of parameter */
comments.  Matter of taste.

> +                                             size, bdrv, sector_size,
> +                                             size >> sector_bits,
> +                                             1      /* width */,
> +                                             0x0000 /* id0 */,
> +                                             0x0000 /* id1 */,
> +                                             0x0000 /* id2 */,
> +                                             0x0000 /* id3 */,
> +                                             0      /* be */);
> +        if (unit == 0) {
> +            flash_mem = pflash_cfi01_get_memory(system_flash);
> +            pc_isa_bios_init(rom_memory, flash_mem, size);
> +        }
>      }
> -
> -    phys_addr = 0x100000000ULL - size;
> -    system_flash = pflash_cfi01_register(phys_addr, NULL, "system.flash", 
> size,
> -                                         bdrv, sector_size, size >> 
> sector_bits,
> -                                         1, 0x0000, 0x0000, 0x0000, 0x0000, 
> 0);
> -    flash_mem = pflash_cfi01_get_memory(system_flash);
> -
> -    pc_isa_bios_init(rom_memory, flash_mem, size);
>  }
>  
>  static void old_pc_system_rom_init(MemoryRegion *rom_memory, bool 
> isapc_ram_fw)
> @@ -181,5 +248,5 @@ void pc_system_firmware_init(MemoryRegion *rom_memory, 
> bool isapc_ram_fw)
>          exit(1);
>      }
>  
> -    pc_system_flash_init(rom_memory, pflash_drv);
> +    pc_system_flash_init(rom_memory);
>  }

Nothing but nits, therefore

Reviewed-by: Markus Armbruster <address@hidden>

Still pining for that star destroyer, though... ;)