Re: [PATCH] physmem: use PR_SET_VMA_ANON_NAME to set ram block name

[David Hildenbrand <david@redhat.com>]

On 11.04.23 06:11, Eiichi Tsukata wrote:
> Use linux specific PR_SET_VMA_ANON_NAME (introduced in v5.17) to set ram
> block name in the kernel. This makes each ram block distinguishable and
> can help debugging and inspection. The names of ram blocks are shown in
> /proc/pid/maps like this:
> 
>    7f00e9400000-7f00f1400000 rw-p 00000000 00:00 0      [anon:pc.ram]
>    7f0115200000-7f0115201000 rw-p 00000000 00:00 0      [anon:/rom@etc/acpi/rsdp]
>    7f0115400000-7f0115410000 rw-p 00000000 00:00 0      [anon:/rom@etc/table-loader]
>    7f0115600000-7f0115800000 rw-p 00000000 00:00 0      [anon:/rom@etc/acpi/tables]
>    7f0115a00000-7f0115a40000 rw-p 00000000 00:00 0      [anon:e1000.rom]
>    ...
> 
> Signed-off-by: Eiichi Tsukata <eiichi.tsukata@nutanix.com>
> ---
>   meson.build       | 2 ++
>   softmmu/physmem.c | 9 +++++++++
>   2 files changed, 11 insertions(+)
> 
> diff --git a/meson.build b/meson.build
> index 29f8644d6d..aca889f5f0 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -2040,6 +2040,8 @@ config_host_data.set('HAVE_OPTRESET',
>                        cc.has_header_symbol('getopt.h', 'optreset'))
>   config_host_data.set('HAVE_IPPROTO_MPTCP',
>                        cc.has_header_symbol('netinet/in.h', 'IPPROTO_MPTCP'))
> +config_host_data.set('CONFIG_PRCTL_PR_SET_VMA_ANON_NAME',
> +                     cc.has_header_symbol('sys/prctl.h', 'PR_SET_VMA_ANON_NAME'))

Nit: I'd suggest placing that directly next to the 
CONFIG_PRCTL_PR_SET_TIMERSLACK check.

>   
>   # has_member
>   config_host_data.set('HAVE_SIGEV_NOTIFY_THREAD_ID',
> diff --git a/softmmu/physmem.c b/softmmu/physmem.c
> index e35061bba4..4fe3e14193 100644
> --- a/softmmu/physmem.c
> +++ b/softmmu/physmem.c
> @@ -80,6 +80,10 @@
>   #include <daxctl/libdaxctl.h>
>   #endif
>   
> +#ifdef CONFIG_PRCTL_PR_SET_VMA_ANON_NAME
> +#include <sys/prctl.h>
> +#endif
> +
>   //#define DEBUG_SUBPAGE
>   
>   /* ram_list is read under rcu_read_lock()/rcu_read_unlock().  Writes
> @@ -1810,6 +1814,11 @@ static void ram_block_add(RAMBlock *new_block, Error **errp)
>                   return;
>               }
>               memory_try_enable_merging(new_block->host, new_block->max_length);
> +#ifdef CONFIG_PRCTL_PR_SET_VMA_ANON_NAME
> +            prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME,
> +                  (unsigned long) new_block->host, new_block->max_length,
> +                  (unsigned long) new_block->mr->name);

We might not have anon memory. I assume that we expect that the prctl 
will simply silently fail (maybe worth a comment) in case we have !anon 
memory.

I assume new_block->mr->name should be set in all cases we care about, 
so LGTM.

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb