Re: [RFC PATCH 4/5] Add migration support for KVM guest with MTE

[Richard Henderson]

On 2/7/21 7:20 PM, Haibo Xu wrote:
> +    if (kvm_physical_memory_addr_from_host(kvm_state, addr, &ipa)) {
> +        /* Buffer for the page tags(one byte per tag) */
> +        tag_buf = g_try_malloc0(size);
> +        if (!tag_buf) {
> +            error_report("%s: Error allocating MTE tag_buf", __func__);
> +            return 0;
> +        }
> +
> +        if (kvm_arm_mte_get_tags(ipa, TARGET_PAGE_SIZE, tag_buf) < 0) {
> +            error_report("%s: Can't get MTE tags from guest", __func__);
> +            g_free(tag_buf);
> +            return 0;
> +        }
> +
> +        qemu_put_buffer(f, tag_buf, size);
> +
> +        g_free(tag_buf);
> +
> +        return size;
> +    }

So, in patch 2 you disabled the allocation of tag-memory.  Now you're
allocating new memory (admittedly quite a small amount -- 1/16th of a page,
small enough to just be a local variable).

Why don't you allocate tag-memory, copy the data into it, and then let
migration proceed as normal.  Then you don't have to have a random data block
that happens to follow each ram page.

I'm concerned that what you're doing here makes it impossible to migrate
between kvm and tcg.


r~