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

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

On Tue, Apr 07, 2020 at 04:17:46PM +0200, Philippe Mathieu-Daudé wrote:
> 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;

I think I prefer the original version though. Matter of taste?

> > +}
> > +
> > +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 {
> >