Re: [Qemu-devel] [PATCH v5 wave 1 2/4] fw-cfg: turn FW_CFG_FILE_SLOTS into a device property

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jan 11, 2017 at 06:34:55PM +0100, Laszlo Ersek wrote:
> We'd like to raise the value of FW_CFG_FILE_SLOTS. Doing it naively could
> lead to problems with backward migration: a more recent QEMU (running an
> older machine type) would allow the guest, in fw_cfg_select(), to select a
> high key value that is unavailable in the same machine type implemented by
> the older (target) QEMU. On the target host, fw_cfg_data_read() for
> example could dereference nonexistent entries.
> 
> As first step, size the FWCfgState.entries[*] and FWCfgState.entry_order
> arrays dynamically. All three array sizes will be influenced by the new
> field (and device property) FWCfgState.file_slots.
> 
> Make the following changes:
> 
> - Replace the FW_CFG_FILE_SLOTS macro with FW_CFG_FILE_SLOTS_MIN (minimum
>   count of fw_cfg file slots) in the header file. The value remains 0x10.
> 
> - Replace all uses of FW_CFG_FILE_SLOTS with a helper function called
>   fw_cfg_file_slots(), returning the new property.
> 
> - Eliminate the macro FW_CFG_MAX_ENTRY, and replace all its uses with a
>   helper function called fw_cfg_max_entry().
> 
> - In the MMIO- and IO-mapped realize functions both, allocate all three
>   arrays dynamically, based on the new property.
> 
> - The new property defaults to FW_CFG_FILE_SLOTS_MIN. This is going to be
>   customized in the following patches.
> 
> Cc: "Gabriel L. Somlo" <somlo@cmu.edu>
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Cc: Igor Mammedov <imammedo@redhat.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
> ---
> 
> Notes:
>     v5:
>     - change the type of "FWCfgState.file_slots" to "uint16_t" [Igor]
>     
>     - same for the retval of the trivial wrapper function
>       fw_cfg_file_slots(), and for the corresponding "file_slots" device
>       properties
>     
>     - preserve the fw_cfg_file_slots() wrapper func (Igor was okay with it
>       in the end)
>     
>     - rename FW_CFG_FILE_SLOTS_TRAD to FW_CFG_FILE_SLOTS_MIN
>     
>     - Remove explicit qdev_prop_set_uint32() calls from fw_cfg_init_io_dma()
>       and fw_cfg_init_mem_wide(), but set the property default to
>       FW_CFG_FILE_SLOTS_MIN (0x10). This is the main change relative to v4;
>       the idea is that per-board opt-in shouldn't be necessary for an
>       increased file_slots count *in addition to* selecting a 2.9 machine
>       type. [Igor]
>     
>     - delay the now-unused FW_CFG_FILE_SLOTS_DFLT macro to a later patch
>     
>     v4:
>     - I know that upstream doesn't care about backward migration, but some
>       downstreams might.
> 
>  docs/specs/fw_cfg.txt          |  2 +-
>  include/hw/nvram/fw_cfg_keys.h |  3 +-
>  hw/nvram/fw_cfg.c              | 71 +++++++++++++++++++++++++++++++++++++-----
>  3 files changed, 65 insertions(+), 11 deletions(-)
> 
> diff --git a/docs/specs/fw_cfg.txt b/docs/specs/fw_cfg.txt
> index a19e2adbe1c6..9373bbc64743 100644
> --- a/docs/specs/fw_cfg.txt
> +++ b/docs/specs/fw_cfg.txt
> @@ -156,7 +156,7 @@ Selector Reg.    Range Usage
>  0xc000 - 0xffff  Arch. Specific (0x0000 - 0x3fff, RW, ignored in v2.4+)
>  
>  In practice, the number of allowed firmware configuration items is given
> -by the value of FW_CFG_MAX_ENTRY (see fw_cfg.h).
> +by the value (FW_CFG_FILE_FIRST + FW_CFG_FILE_SLOTS_MIN) (see fw_cfg.h).
>  
>  = Guest-side DMA Interface =
>  
> diff --git a/include/hw/nvram/fw_cfg_keys.h b/include/hw/nvram/fw_cfg_keys.h
> index 0f3e871884c0..b6919451f5bd 100644
> --- a/include/hw/nvram/fw_cfg_keys.h
> +++ b/include/hw/nvram/fw_cfg_keys.h
> @@ -29,8 +29,7 @@
>  #define FW_CFG_FILE_DIR         0x19
>  
>  #define FW_CFG_FILE_FIRST       0x20
> -#define FW_CFG_FILE_SLOTS       0x10
> -#define FW_CFG_MAX_ENTRY        (FW_CFG_FILE_FIRST + FW_CFG_FILE_SLOTS)
> +#define FW_CFG_FILE_SLOTS_MIN   0x10
>  
>  #define FW_CFG_WRITE_CHANNEL    0x4000
>  #define FW_CFG_ARCH_LOCAL       0x8000
> diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
> index e0145c11a19b..313d943ebd27 100644
> --- a/hw/nvram/fw_cfg.c
> +++ b/hw/nvram/fw_cfg.c
> @@ -33,6 +33,7 @@
>  #include "qemu/error-report.h"
>  #include "qemu/config-file.h"
>  #include "qemu/cutils.h"
> +#include "qapi/error.h"
>  
>  #define FW_CFG_NAME "fw_cfg"
>  #define FW_CFG_PATH "/machine/" FW_CFG_NAME
> @@ -71,8 +72,9 @@ struct FWCfgState {
>      SysBusDevice parent_obj;
>      /*< public >*/
>  
> -    FWCfgEntry entries[2][FW_CFG_MAX_ENTRY];
> -    int entry_order[FW_CFG_MAX_ENTRY];
> +    uint16_t file_slots;
> +    FWCfgEntry *entries[2];
> +    int *entry_order;
>      FWCfgFiles *files;
>      uint16_t cur_entry;
>      uint32_t cur_offset;
> @@ -257,13 +259,24 @@ static void fw_cfg_write(FWCfgState *s, uint8_t value)
>      /* nothing, write support removed in QEMU v2.4+ */
>  }
>  
> +static inline uint16_t fw_cfg_file_slots(const FWCfgState *s)
> +{
> +    return s->file_slots;
> +}
> +
> +/* Note: this function returns an exclusive limit. */
> +static inline uint32_t fw_cfg_max_entry(const FWCfgState *s)
> +{
> +    return FW_CFG_FILE_FIRST + fw_cfg_file_slots(s);
> +}
> +
>  static int fw_cfg_select(FWCfgState *s, uint16_t key)
>  {
>      int arch, ret;
>      FWCfgEntry *e;
>  
>      s->cur_offset = 0;
> -    if ((key & FW_CFG_ENTRY_MASK) >= FW_CFG_MAX_ENTRY) {
> +    if ((key & FW_CFG_ENTRY_MASK) >= fw_cfg_max_entry(s)) {
>          s->cur_entry = FW_CFG_INVALID;
>          ret = 0;
>      } else {
> @@ -610,7 +623,7 @@ static void fw_cfg_add_bytes_read_callback(FWCfgState *s, uint16_t key,
>  
>      key &= FW_CFG_ENTRY_MASK;
>  
> -    assert(key < FW_CFG_MAX_ENTRY && len < UINT32_MAX);
> +    assert(key < fw_cfg_max_entry(s) && len < UINT32_MAX);
>      assert(s->entries[arch][key].data == NULL); /* avoid key conflict */
>  
>      s->entries[arch][key].data = data;
> @@ -628,7 +641,7 @@ static void *fw_cfg_modify_bytes_read(FWCfgState *s, uint16_t key,
>  
>      key &= FW_CFG_ENTRY_MASK;
>  
> -    assert(key < FW_CFG_MAX_ENTRY && len < UINT32_MAX);
> +    assert(key < fw_cfg_max_entry(s) && len < UINT32_MAX);
>  
>      /* return the old data to the function caller, avoid memory leak */
>      ptr = s->entries[arch][key].data;
> @@ -777,13 +790,13 @@ void fw_cfg_add_file_callback(FWCfgState *s,  const char *filename,
>      int order = 0;
>  
>      if (!s->files) {
> -        dsize = sizeof(uint32_t) + sizeof(FWCfgFile) * FW_CFG_FILE_SLOTS;
> +        dsize = sizeof(uint32_t) + sizeof(FWCfgFile) * fw_cfg_file_slots(s);
>          s->files = g_malloc0(dsize);
>          fw_cfg_add_bytes(s, FW_CFG_FILE_DIR, s->files, dsize);
>      }
>  
>      count = be32_to_cpu(s->files->count);
> -    assert(count < FW_CFG_FILE_SLOTS);
> +    assert(count < fw_cfg_file_slots(s));
>  
>      /* Find the insertion point. */
>      if (mc->legacy_fw_cfg_order) {
> @@ -857,7 +870,7 @@ void *fw_cfg_modify_file(FWCfgState *s, const char *filename,
>      assert(s->files);
>  
>      index = be32_to_cpu(s->files->count);
> -    assert(index < FW_CFG_FILE_SLOTS);
> +    assert(index < fw_cfg_file_slots(s));
>  
>      for (i = 0; i < index; i++) {
>          if (strcmp(filename, s->files->f[i].name) == 0) {
> @@ -1014,12 +1027,38 @@ static const TypeInfo fw_cfg_info = {
>      .class_init    = fw_cfg_class_init,
>  };
>  
> +static void fw_cfg_file_slots_allocate(FWCfgState *s, Error **errp)
> +{
> +    uint16_t file_slots_max;
> +
> +    if (fw_cfg_file_slots(s) < FW_CFG_FILE_SLOTS_MIN) {
> +        error_setg(errp, "\"file_slots\" must be at least 0x%x",
> +                   FW_CFG_FILE_SLOTS_MIN);
> +        return;
> +    }
> +
> +    /* (UINT16_MAX & FW_CFG_ENTRY_MASK) is the highest inclusive selector value
> +     * that we permit. The actual (exclusive) value coming from the
> +     * configuration is (FW_CFG_FILE_FIRST + fw_cfg_file_slots(s)). */
> +    file_slots_max = (UINT16_MAX & FW_CFG_ENTRY_MASK) - FW_CFG_FILE_FIRST + 1;
> +    if (fw_cfg_file_slots(s) > file_slots_max) {
> +        error_setg(errp, "\"file_slots\" must not exceed 0x%" PRIx16,
> +                   file_slots_max);
> +        return;
> +    }
> +
> +    s->entries[0] = g_new0(FWCfgEntry, fw_cfg_max_entry(s));
> +    s->entries[1] = g_new0(FWCfgEntry, fw_cfg_max_entry(s));
> +    s->entry_order = g_new0(int, fw_cfg_max_entry(s));
> +}
>  
>  static Property fw_cfg_io_properties[] = {
>      DEFINE_PROP_UINT32("iobase", FWCfgIoState, iobase, -1),
>      DEFINE_PROP_UINT32("dma_iobase", FWCfgIoState, dma_iobase, -1),
>      DEFINE_PROP_BOOL("dma_enabled", FWCfgIoState, parent_obj.dma_enabled,
>                       true),
> +    DEFINE_PROP_UINT16("file_slots", FWCfgIoState, parent_obj.file_slots,
> +                       FW_CFG_FILE_SLOTS_MIN),
>      DEFINE_PROP_END_OF_LIST(),
>  };
>  
> @@ -1027,6 +1066,13 @@ static void fw_cfg_io_realize(DeviceState *dev, Error **errp)
>  {
>      FWCfgIoState *s = FW_CFG_IO(dev);
>      SysBusDevice *sbd = SYS_BUS_DEVICE(dev);
> +    Error *local_err = NULL;
> +
> +    fw_cfg_file_slots_allocate(FW_CFG(s), &local_err);
> +    if (local_err) {
> +        error_propagate(errp, local_err);
> +        return;
> +    }
>  
>      /* when using port i/o, the 8-bit data register ALWAYS overlaps
>       * with half of the 16-bit control register. Hence, the total size
> @@ -1063,6 +1109,8 @@ static Property fw_cfg_mem_properties[] = {
>      DEFINE_PROP_UINT32("data_width", FWCfgMemState, data_width, -1),
>      DEFINE_PROP_BOOL("dma_enabled", FWCfgMemState, parent_obj.dma_enabled,
>                       true),
> +    DEFINE_PROP_UINT16("file_slots", FWCfgMemState, parent_obj.file_slots,
> +                       FW_CFG_FILE_SLOTS_MIN),

I think it's an internal compatibility thing, so we want to call it
x-file-slots instead.


>      DEFINE_PROP_END_OF_LIST(),
>  };
>  
> @@ -1071,6 +1119,13 @@ static void fw_cfg_mem_realize(DeviceState *dev, Error **errp)
>      FWCfgMemState *s = FW_CFG_MEM(dev);
>      SysBusDevice *sbd = SYS_BUS_DEVICE(dev);
>      const MemoryRegionOps *data_ops = &fw_cfg_data_mem_ops;
> +    Error *local_err = NULL;
> +
> +    fw_cfg_file_slots_allocate(FW_CFG(s), &local_err);
> +    if (local_err) {
> +        error_propagate(errp, local_err);
> +        return;
> +    }
>  
>      memory_region_init_io(&s->ctl_iomem, OBJECT(s), &fw_cfg_ctl_mem_ops,
>                            FW_CFG(s), "fwcfg.ctl", FW_CFG_CTL_SIZE);
> -- 
> 2.9.3
>