Re: [Qemu-devel] [PATCH] migration: check length directly to make sure the range is aligned

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
To: Wei Yang <richardw.yang@linux.intel.com>, rth@twiddle.net
Cc: pbonzini@redhat.com, qemu-devel@nongnu.org, quintela@redhat.com
Subject: Re: [Qemu-devel] [PATCH] migration: check length directly to make sure the range is aligned
Date: Fri, 19 Jul 2019 18:54:00 +0100	[thread overview]
Message-ID: <20190719175400.GJ3000@work-vm> (raw)
In-Reply-To: <20190712032704.7826-1-richardw.yang@linux.intel.com>

* Wei Yang (richardw.yang@linux.intel.com) wrote:
> Since the start addr is already checked, to make sure the range is
> aligned, checking the length is enough.
> 
> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
> ---
>  exec.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index 50ea9c5aaa..8fa980baae 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -4067,10 +4067,9 @@ int ram_block_discard_range(RAMBlock *rb, uint64_t start, size_t length)
>  
>      if ((start + length) <= rb->used_length) {
>          bool need_madvise, need_fallocate;
> -        uint8_t *host_endaddr = host_startaddr + length;
> -        if ((uintptr_t)host_endaddr & (rb->page_size - 1)) {
> -            error_report("ram_block_discard_range: Unaligned end address: %p",
> -                         host_endaddr);
> +        if (length & (rb->page_size - 1)) {
> +            error_report("ram_block_discard_range: Unaligned length: %lx",
> +                         length);

Yes, I *think* this is safe, we'll need to watch out for any warnings;
David Gibson's balloon fix from February means that the balloon code
should now warn in it's case.

rth: Want to pick this up?

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

>              goto err;
>          }
>  
> -- 
> 2.17.1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK