Re: [Xen-devel] [PATCH v9 12/15] microcode: reduce memory allocation and copy when creating a patch

["Roger Pau Monné" <roger.pau@citrix.com>]

On Mon, Aug 19, 2019 at 09:25:25AM +0800, Chao Gao wrote:
> To create a microcode patch from a vendor-specific update,
> allocate_microcode_patch() copied everything from the update.
> It is not efficient. Essentially, we just need to go through
> ucodes in the blob, find the one with the newest revision and
> install it into the microcode_patch. In the process, buffers
> like mc_amd, equiv_cpu_table (on AMD side), and mc (on Intel
> side) can be reused. microcode_patch now is allocated after
> it is sure that there is a matching ucode.

Oh, I think this answers my question on a previous patch.

For future series it would be nice to avoid so many rewrites in the
same series, alloc_microcode_patch is already modified in a previous
patch, just to be removed here. It also makes it harder to follow
what's going on.

> 
> Signed-off-by: Chao Gao <chao.gao@intel.com>
> ---
> Changes in v9:
>  - new
> ---
>  xen/arch/x86/microcode_amd.c   | 99 +++++++++++++++---------------------------
>  xen/arch/x86/microcode_intel.c | 65 ++++++++++-----------------
>  2 files changed, 58 insertions(+), 106 deletions(-)
> 
> diff --git a/xen/arch/x86/microcode_amd.c b/xen/arch/x86/microcode_amd.c
> index 6353323..ec1c2eb 100644
> --- a/xen/arch/x86/microcode_amd.c
> +++ b/xen/arch/x86/microcode_amd.c
> @@ -194,36 +194,6 @@ static bool match_cpu(const struct microcode_patch *patch)
>      return patch && (microcode_fits(patch->mc_amd) == NEW_UCODE);
>  }
>  
> -static struct microcode_patch *alloc_microcode_patch(
> -    const struct microcode_amd *mc_amd)
> -{
> -    struct microcode_patch *microcode_patch = xmalloc(struct microcode_patch);
> -    struct microcode_amd *cache = xmalloc(struct microcode_amd);
> -    void *mpb = xmalloc_bytes(mc_amd->mpb_size);
> -    struct equiv_cpu_entry *equiv_cpu_table =
> -                                xmalloc_bytes(mc_amd->equiv_cpu_table_size);
> -
> -    if ( !microcode_patch || !cache || !mpb || !equiv_cpu_table )
> -    {
> -        xfree(microcode_patch);
> -        xfree(cache);
> -        xfree(mpb);
> -        xfree(equiv_cpu_table);
> -        return ERR_PTR(-ENOMEM);
> -    }
> -
> -    memcpy(mpb, mc_amd->mpb, mc_amd->mpb_size);
> -    cache->mpb = mpb;
> -    cache->mpb_size = mc_amd->mpb_size;
> -    memcpy(equiv_cpu_table, mc_amd->equiv_cpu_table,
> -           mc_amd->equiv_cpu_table_size);
> -    cache->equiv_cpu_table = equiv_cpu_table;
> -    cache->equiv_cpu_table_size = mc_amd->equiv_cpu_table_size;
> -    microcode_patch->mc_amd = cache;
> -
> -    return microcode_patch;
> -}
> -
>  static void free_patch(void *mc)
>  {
>      struct microcode_amd *mc_amd = mc;
> @@ -320,18 +290,10 @@ static int get_ucode_from_buffer_amd(
>          return -EINVAL;
>      }
>  
> -    if ( mc_amd->mpb_size < mpbuf->len )
> -    {
> -        if ( mc_amd->mpb )
> -        {
> -            xfree(mc_amd->mpb);
> -            mc_amd->mpb_size = 0;
> -        }
> -        mc_amd->mpb = xmalloc_bytes(mpbuf->len);
> -        if ( mc_amd->mpb == NULL )
> -            return -ENOMEM;
> -        mc_amd->mpb_size = mpbuf->len;
> -    }
> +    mc_amd->mpb = xmalloc_bytes(mpbuf->len);
> +    if ( mc_amd->mpb == NULL )

Nit:

if ( !mc_amd->mpb )

is the usual idiom used in Xen.

> +        return -ENOMEM;
> +    mc_amd->mpb_size = mpbuf->len;
>      memcpy(mc_amd->mpb, mpbuf->data, mpbuf->len);
>  
>      pr_debug("microcode: CPU%d size %zu, block size %u offset %zu equivID %#x rev %#x\n",
> @@ -451,8 +413,9 @@ static struct microcode_patch *cpu_request_microcode(const void *buf,
>                                                       size_t bufsize)
>  {
>      struct microcode_amd *mc_amd;
> +    struct microcode_header_amd *saved = NULL;
>      struct microcode_patch *patch = NULL;
> -    size_t offset = 0;
> +    size_t offset = 0, saved_size = 0;
>      int error = 0;
>      unsigned int current_cpu_id;
>      unsigned int equiv_cpu_id;
> @@ -542,29 +505,21 @@ static struct microcode_patch *cpu_request_microcode(const void *buf,
>      while ( (error = get_ucode_from_buffer_amd(mc_amd, buf, bufsize,
>                                                 &offset)) == 0 )
>      {
> -        struct microcode_patch *new_patch = alloc_microcode_patch(mc_amd);
> -
> -        if ( IS_ERR(new_patch) )
> -        {
> -            error = PTR_ERR(new_patch);
> -            break;
> -        }
> -
>          /*
> -         * If the new patch covers current CPU, compare patches and store the
> +         * If the new ucode covers current CPU, compare ucodes and store the
>           * one with higher revision.
>           */
> -        if ( (microcode_fits(new_patch->mc_amd) != MIS_UCODE) &&
> -             (!patch || (compare_patch(new_patch, patch) == NEW_UCODE)) )
> +#define REV_ID(mpb) (((struct microcode_header_amd *)(mpb))->processor_rev_id)
> +        if ( (microcode_fits(mc_amd) != MIS_UCODE) &&
> +             (!saved || (REV_ID(mc_amd->mpb) > REV_ID(saved))) )
> +#undef REV_ID
>          {
> -            struct microcode_patch *tmp = patch;
> -
> -            patch = new_patch;
> -            new_patch = tmp;
> +            xfree(saved);
> +            saved = mc_amd->mpb;
> +            saved_size = mc_amd->mpb_size;
>          }
> -
> -        if ( new_patch )
> -            microcode_free_patch(new_patch);
> +        else
> +            xfree(mc_amd->mpb);
>  
>          if ( offset >= bufsize )
>              break;
> @@ -593,9 +548,25 @@ static struct microcode_patch *cpu_request_microcode(const void *buf,
>               *(const uint32_t *)(buf + offset) == UCODE_MAGIC )
>              break;
>      }
> -    xfree(mc_amd->mpb);
> -    xfree(mc_amd->equiv_cpu_table);
> -    xfree(mc_amd);
> +
> +    if ( saved )
> +    {
> +        mc_amd->mpb = saved;
> +        mc_amd->mpb_size = saved_size;
> +        patch = xmalloc(struct microcode_patch);
> +        if ( patch )
> +            patch->mc_amd = mc_amd;
> +        else
> +        {
> +            free_patch(mc_amd);
> +            error = -ENOMEM;
> +        }
> +    }
> +    else
> +    {
> +        mc_amd->mpb = NULL;

What's the point in setting mpb to NULL if you are just going to free
mc_amd below?

Also, I'm not sure I understand why you need to free mc_amd, isn't
this buff memory that should be freed by the caller?

ie: in the Intel counterpart below you don't seem to free the mc
cursor used for the get_next_ucode_from_buffer loop.

> +        free_patch(mc_amd);
> +    }
>  
>    out:
>      if ( error && !patch )
> diff --git a/xen/arch/x86/microcode_intel.c b/xen/arch/x86/microcode_intel.c
> index 96b38f8..ae5759f 100644
> --- a/xen/arch/x86/microcode_intel.c
> +++ b/xen/arch/x86/microcode_intel.c
> @@ -282,25 +282,6 @@ static enum microcode_match_result compare_patch(
>                                                                  OLD_UCODE;
>  }
>  
> -static struct microcode_patch *alloc_microcode_patch(
> -    const struct microcode_header_intel *mc_header)
> -{
> -    unsigned long total_size = get_totalsize(mc_header);
> -    void *new_mc = xmalloc_bytes(total_size);
> -    struct microcode_patch *new_patch = xmalloc(struct microcode_patch);
> -
> -    if ( !new_patch || !new_mc )
> -    {
> -        xfree(new_patch);
> -        xfree(new_mc);
> -        return ERR_PTR(-ENOMEM);
> -    }
> -    memcpy(new_mc, mc_header, total_size);
> -    new_patch->mc_intel = new_mc;
> -
> -    return new_patch;
> -}
> -
>  static int apply_microcode(const struct microcode_patch *patch)
>  {
>      unsigned long flags;
> @@ -379,47 +360,47 @@ static struct microcode_patch *cpu_request_microcode(const void *buf,
>  {
>      long offset = 0;
>      int error = 0;
> -    void *mc;
> +    struct microcode_intel *mc, *saved = NULL;
>      struct microcode_patch *patch = NULL;
>  
> -    while ( (offset = get_next_ucode_from_buffer(&mc, buf, size, offset)) > 0 )
> +    while ( (offset = get_next_ucode_from_buffer((void **)&mc, buf,
> +                                                 size, offset)) > 0 )
>      {
> -        struct microcode_patch *new_patch;
> -
>          error = microcode_sanity_check(mc);
>          if ( error )
> -            break;
> -
> -        new_patch = alloc_microcode_patch(mc);
> -        if ( IS_ERR(new_patch) )
>          {
> -            error = PTR_ERR(new_patch);
> +            xfree(mc);
>              break;
>          }
>  
>          /*
> -         * If the new patch covers current CPU, compare patches and store the
> +         * If the new update covers current CPU, compare updates and store the
>           * one with higher revision.
>           */
> -        if ( (microcode_update_match(&new_patch->mc_intel->hdr) != MIS_UCODE) &&
> -             (!patch || (compare_patch(new_patch, patch) == NEW_UCODE)) )
> +        if ( (microcode_update_match(&mc->hdr) != MIS_UCODE) &&
> +             (!saved || (mc->hdr.rev > saved->hdr.rev)) )
>          {
> -            struct microcode_patch *tmp = patch;
> -
> -            patch = new_patch;
> -            new_patch = tmp;
> +            xfree(saved);
> +            saved = mc;
>          }
> -
> -        if ( new_patch )
> -            microcode_free_patch(new_patch);
> -
> -        xfree(mc);
> +        else
> +            xfree(mc);
>      }
> -    if ( offset > 0 )
> -        xfree(mc);
>      if ( offset < 0 )
>          error = offset;
>  
> +    if ( saved )
> +    {
> +        patch = xmalloc(struct microcode_patch);
> +        if ( patch )
> +            patch->mc_intel = saved;
> +        else
> +        {
> +            xfree(saved);
> +            error = -ENOMEM;
> +        }
> +    }
> +

The above code looks suspiciously similar to the AMD
cpu_request_microcode counterpart, which makes me think it could be
further abstracted in order to reduce this duplication. In any case,
this can be done in a follow up patch.

Thanks, Roger.

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