Re: [PATCH for-5.0 v2 2/3] fw_cfg: Migrate ACPI table mr sizes separately

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 4/3/20 12:18 PM, Shameer Kolothum wrote:
> Any sub-page size update to ACPI MRs will be lost during
> migration, as we use aligned size in ram_load_precopy() ->
> qemu_ram_resize() path. This will result in inconsistency in
> FWCfgEntry sizes between source and destination. In order to avoid
> this, save and restore them separately during migration.
> 
> Up until now, this problem may not be that relevant for x86 as both
> ACPI table and Linker MRs gets padded and aligned. Also at present,
> qemu_ram_resize() doesn't invoke callback to update FWCfgEntry for
> unaligned size changes. But since we are going to fix the
> qemu_ram_resize() in the subsequent patch, the issue may become
> more serious especially for RSDP MR case.
> 
> Moreover, the issue will soon become prominent in arm/virt as well
> where the MRs are not padded or aligned at all and eventually have
> acpi table changes as part of future additions like NVDIMM hot-add
> feature.
> 
> Suggested-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
> Acked-by: David Hildenbrand <david@redhat.com>
> ---
> v1 --> v2
>   - Changed *_mr_size from size_t to uint64_t to address portability.
>   - post_copy only done if sizes are not aligned.
> 
> Please find previous discussions here,
> https://patchwork.kernel.org/patch/11339591/#23140343
> ---
>   hw/core/machine.c         |  1 +
>   hw/nvram/fw_cfg.c         | 91 ++++++++++++++++++++++++++++++++++++++-
>   include/hw/nvram/fw_cfg.h |  6 +++
>   3 files changed, 97 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index de0c425605..c1a444cb75 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -39,6 +39,7 @@ GlobalProperty hw_compat_4_2[] = {
>       { "usb-redir", "suppress-remote-wake", "off" },
>       { "qxl", "revision", "4" },
>       { "qxl-vga", "revision", "4" },
> +    { "fw_cfg", "acpi-mr-restore", "false" },
>   };
>   const size_t hw_compat_4_2_len = G_N_ELEMENTS(hw_compat_4_2);
>   
> diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
> index 179b302f01..4be6c9d9fd 100644
> --- a/hw/nvram/fw_cfg.c
> +++ b/hw/nvram/fw_cfg.c
> @@ -39,6 +39,7 @@
>   #include "qemu/config-file.h"
>   #include "qemu/cutils.h"
>   #include "qapi/error.h"
> +#include "hw/acpi/aml-build.h"
>   
>   #define FW_CFG_FILE_SLOTS_DFLT 0x20
>   
> @@ -610,6 +611,55 @@ bool fw_cfg_dma_enabled(void *opaque)
>       return s->dma_enabled;
>   }
>   
> +static bool fw_cfg_acpi_mr_restore(void *opaque)
> +{
> +    FWCfgState *s = opaque;
> +    bool mr_aligned;
> +
> +    mr_aligned = QEMU_IS_ALIGNED(s->table_mr_size, qemu_real_host_page_size) &&
> +                 QEMU_IS_ALIGNED(s->linker_mr_size, qemu_real_host_page_size) &&
> +                 QEMU_IS_ALIGNED(s->rsdp_mr_size, qemu_real_host_page_size);
> +    return s->acpi_mr_restore && !mr_aligned;

This code is hard to review.

Is this equivalent?

     if (!s->acpi_mr_restore) {
         return false;
     }
     if (!QEMU_IS_ALIGNED(s->table_mr_size, qemu_real_host_page_size)) {
         return false;
     }
     if (!QEMU_IS_ALIGNED(s->linker_mr_size, qemu_real_host_page_size)) {
         return false;
     }
     if (!QEMU_IS_ALIGNED(s->rsdp_mr_size, qemu_real_host_page_size)) {
         return false;
     }
     return true;

> +}
> +
> +static void fw_cfg_update_mr(FWCfgState *s, uint16_t key, size_t size)
> +{
> +    MemoryRegion *mr;
> +    ram_addr_t offset;
> +    int arch = !!(key & FW_CFG_ARCH_LOCAL);
> +    void *ptr;
> +
> +    key &= FW_CFG_ENTRY_MASK;
> +    assert(key < fw_cfg_max_entry(s));
> +
> +    ptr = s->entries[arch][key].data;
> +    mr = memory_region_from_host(ptr, &offset);
> +
> +    memory_region_ram_resize(mr, size, &error_abort);
> +}
> +
> +static int fw_cfg_acpi_mr_restore_post_load(void *opaque, int version_id)
> +{
> +    FWCfgState *s = opaque;
> +    int i, index;
> +
> +    assert(s->files);
> +
> +    index = be32_to_cpu(s->files->count);
> +
> +    for (i = 0; i < index; i++) {
> +        if (!strcmp(s->files->f[i].name, ACPI_BUILD_TABLE_FILE)) {
> +            fw_cfg_update_mr(s, FW_CFG_FILE_FIRST + i, s->table_mr_size);
> +        } else if (!strcmp(s->files->f[i].name, ACPI_BUILD_LOADER_FILE)) {
> +            fw_cfg_update_mr(s, FW_CFG_FILE_FIRST + i, s->linker_mr_size);
> +        } else if (!strcmp(s->files->f[i].name, ACPI_BUILD_RSDP_FILE)) {
> +            fw_cfg_update_mr(s, FW_CFG_FILE_FIRST + i, s->rsdp_mr_size);
> +        }
> +    }
> +
> +    return 0;
> +}
> +
>   static const VMStateDescription vmstate_fw_cfg_dma = {
>       .name = "fw_cfg/dma",
>       .needed = fw_cfg_dma_enabled,
> @@ -619,6 +669,20 @@ static const VMStateDescription vmstate_fw_cfg_dma = {
>       },
>   };
>   
> +static const VMStateDescription vmstate_fw_cfg_acpi_mr = {
> +    .name = "fw_cfg/acpi_mr",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .needed = fw_cfg_acpi_mr_restore,
> +    .post_load = fw_cfg_acpi_mr_restore_post_load,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_UINT64(table_mr_size, FWCfgState),
> +        VMSTATE_UINT64(linker_mr_size, FWCfgState),
> +        VMSTATE_UINT64(rsdp_mr_size, FWCfgState),
> +        VMSTATE_END_OF_LIST()
> +    },
> +};
> +
>   static const VMStateDescription vmstate_fw_cfg = {
>       .name = "fw_cfg",
>       .version_id = 2,
> @@ -631,6 +695,7 @@ static const VMStateDescription vmstate_fw_cfg = {
>       },
>       .subsections = (const VMStateDescription*[]) {
>           &vmstate_fw_cfg_dma,
> +        &vmstate_fw_cfg_acpi_mr,
>           NULL,
>       }
>   };
> @@ -815,6 +880,23 @@ static struct {
>   #define FW_CFG_ORDER_OVERRIDE_LAST 200
>   };
>   
> +/*
> + * Any sub-page size update to these table MRs will be lost during migration,
> + * as we use aligned size in ram_load_precopy() -> qemu_ram_resize() path.
> + * In order to avoid the inconsistency in sizes save them seperately and
> + * migrate over in vmstate post_load().
> + */
> +static void fw_cfg_acpi_mr_save(FWCfgState *s, const char *filename, size_t len)
> +{
> +    if (!strcmp(filename, ACPI_BUILD_TABLE_FILE)) {
> +        s->table_mr_size = len;
> +    } else if (!strcmp(filename, ACPI_BUILD_LOADER_FILE)) {
> +        s->linker_mr_size = len;
> +    } else if (!strcmp(filename, ACPI_BUILD_RSDP_FILE)) {
> +        s->rsdp_mr_size = len;
> +    }
> +}
> +
>   static int get_fw_cfg_order(FWCfgState *s, const char *name)
>   {
>       int i;
> @@ -914,6 +996,7 @@ void fw_cfg_add_file_callback(FWCfgState *s,  const char *filename,
>       trace_fw_cfg_add_file(s, index, s->files->f[index].name, len);
>   
>       s->files->count = cpu_to_be32(count+1);
> +    fw_cfg_acpi_mr_save(s, filename, len);
>   }
>   
>   void fw_cfg_add_file(FWCfgState *s,  const char *filename,
> @@ -937,6 +1020,7 @@ void *fw_cfg_modify_file(FWCfgState *s, const char *filename,
>               ptr = fw_cfg_modify_bytes_read(s, FW_CFG_FILE_FIRST + i,
>                                              data, len);
>               s->files->f[i].size   = cpu_to_be32(len);
> +            fw_cfg_acpi_mr_save(s, filename, len);
>               return ptr;
>           }
>       }
> @@ -973,7 +1057,10 @@ static void fw_cfg_machine_ready(struct Notifier *n, void *data)
>       qemu_register_reset(fw_cfg_machine_reset, s);
>   }
>   
> -
> +static Property fw_cfg_properties[] = {
> +    DEFINE_PROP_BOOL("acpi-mr-restore", FWCfgState, acpi_mr_restore, true),
> +    DEFINE_PROP_END_OF_LIST(),
> +};
>   
>   static void fw_cfg_common_realize(DeviceState *dev, Error **errp)
>   {
> @@ -1097,6 +1184,8 @@ static void fw_cfg_class_init(ObjectClass *klass, void *data)
>   
>       dc->reset = fw_cfg_reset;
>       dc->vmsd = &vmstate_fw_cfg;
> +
> +    device_class_set_props(dc, fw_cfg_properties);
>   }
>   
>   static const TypeInfo fw_cfg_info = {
> diff --git a/include/hw/nvram/fw_cfg.h b/include/hw/nvram/fw_cfg.h
> index b5291eefad..25d9307018 100644
> --- a/include/hw/nvram/fw_cfg.h
> +++ b/include/hw/nvram/fw_cfg.h
> @@ -53,6 +53,12 @@ struct FWCfgState {
>       dma_addr_t dma_addr;
>       AddressSpace *dma_as;
>       MemoryRegion dma_iomem;
> +
> +    /* restore during migration */
> +    bool acpi_mr_restore;
> +    uint64_t table_mr_size;
> +    uint64_t linker_mr_size;
> +    uint64_t rsdp_mr_size;
>   };
>   
>   struct FWCfgIoState {
>