Re: [PATCH v3 03/10] exec: Fix for qemu_ram_resize() callback

[David Hildenbrand <david@redhat.com>]

On 11.03.20 18:20, Shameer Kolothum wrote:
> From: David Hildenbrand <david@redhat.com>
> 
> Summarizing the issue:
> 1. Memory regions contain ram blocks with a different size,  if the
>    size is  not properly aligned. While memory regions can have an
>    unaligned size, ram blocks can't. This is true when creating
>    resizable memory region with  an unaligned size.
> 2. When resizing a ram block/memory region, the size of the memory
>    region  is set to the aligned size. The callback is called with
>    the aligned size. The unaligned piece is lost.
> 
> Because of the above, if ACPI blob length modifications happens
> after the initial virt_acpi_build() call, and the changed blob
> length is within the PAGE size boundary, then the revised size
> is not seen by the firmware on Guest reboot.
> 
> Hence make sure callback is called if memory region size is changed,
> irrespective of aligned or not.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>
> [Shameer: added commit log]
> Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
> ---
> Please find the discussion here,
> https://patchwork.kernel.org/patch/11339591/
> ---
>  exec.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index 0cc500d53a..f8974cd303 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2073,11 +2073,21 @@ static int memory_try_enable_merging(void *addr, size_t len)
>   */
>  int qemu_ram_resize(RAMBlock *block, ram_addr_t newsize, Error **errp)
>  {
> +    const ram_addr_t unaligned_size = newsize;
> +
>      assert(block);
>  
>      newsize = HOST_PAGE_ALIGN(newsize);
>  
>      if (block->used_length == newsize) {
> +        /*
> +         * We don't have to resize the ram block (which only knows aligned
> +         * sizes), however, we have to notify if the unaligned size changed.
> +         */
> +        if (block->resized && unaligned_size != memory_region_size(block->mr)) {
> +            block->resized(block->idstr, unaligned_size, block->host);
> +            memory_region_set_size(block->mr, unaligned_size);
> +        }

I guess we should do

if (unaligned_size != memory_region_size(block->mr)) {
    memory_region_set_size(block->mr, unaligned_size);
    if (block->resized) {
        block->resized(block->idstr, unaligned_size, block->host);
    }
}

Instead - like in the case below.


Note: This is not completely clean, the RAM block code should'n have to
care about unaligned stuff. Also, the resized() callback for the RAM
block is ugly, it should be a resized callback for the memory region.
But these things imply requires bigger refactorings, so I guess this is
good and simple enough for now.

-- 
Thanks,

David / dhildenb