On 04/06/2016 04:44 AM, Bharata B Rao wrote:
> memory_hotplug_max() uses hot_add_drconf_memory_max() to get maxmimum
> addressable memory by referring to ibm,dyanamic-memory property. There
> are three problems with the current approach:
>
> 1 hot_add_drconf_memory_max() assumes that ibm,dynamic-memory includes
> all the LMBs of the guest, but that is not true for PowerKVM which
> populates only DR LMBs (LMBs that can be hotplugged/removed) in that
> property.
> 2 hot_add_drconf_memory_max() multiplies lmb-size with lmb-count to arrive
> at the max possible address. Since ibm,dynamic-memory doesn't include
> RMA LMBs, the address thus obtained will be less than the actual max
> address. For example, if max possible memory size is 32G, with lmb-size
> of 256MB there can be 127 LMBs in ibm,dynamic-memory (1 LMB for RMA
> which won't be present here). hot_add_drconf_memory_max() would then
> return the max addressable memory as 127 * 256MB = 31.75GB, the max
> address should have been 32G which is what ibm,lrdr-capacity shows.
> 3 In PowerKVM, there can be a gap between the end of boot time RAM and
> beginning of hotplug RAM area. So just multiplying lmb-count with
> lmb-size will not provide the correct max possible address for PowerKVM.
>
> This patch fixes 1 by using ibm,lrdr-capacity property to return the max
> addressable memory whenever the property is present. Then it fixes 2 & 3
> by fetching the address of the last LMB in ibm,dynamic-memory property.
>
> NOTE: There are some unnecessary changes in the patch because of converting
> spaces to tabs w/o which checkpatch.pl complains.
>
> Signed-off-by: Bharata B Rao <bhar...@linux.vnet.ibm.com>
> ---
> arch/powerpc/mm/numa.c | 29 ++++++++++++++++++++++-------
> 1 file changed, 22 insertions(+), 7 deletions(-)
>
> diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
> index 669a15e..57d5877 100644
> --- a/arch/powerpc/mm/numa.c
> +++ b/arch/powerpc/mm/numa.c
> @@ -1164,17 +1164,32 @@ int hot_add_scn_to_nid(unsigned long scn_addr)
> static u64 hot_add_drconf_memory_max(void)
> {
> struct device_node *memory = NULL;
> - unsigned int drconf_cell_cnt = 0;
> - u64 lmb_size = 0;
> + struct device_node *dn = NULL;
> + unsigned int drconf_cell_cnt = 0;
> + u64 lmb_size = 0;
> const __be32 *dm = NULL;
> + const __be64 *lrdr = NULL;
> + struct of_drconf_cell drmem;
> +
> + dn = of_find_node_by_path("/rtas");
> + if (dn) {
> + lrdr = of_get_property(dn, "ibm,lrdr-capacity", NULL);
> + of_node_put(dn);
> + if (lrdr)
> + return be64_to_cpup(lrdr);
> + }
>
> memory = of_find_node_by_path("/ibm,dynamic-reconfiguration-memory");
> if (memory) {
> - drconf_cell_cnt = of_get_drconf_memory(memory, &dm);
> - lmb_size = of_get_lmb_size(memory);
> - of_node_put(memory);
> - }
> - return lmb_size * drconf_cell_cnt;
> + drconf_cell_cnt = of_get_drconf_memory(memory, &dm);
> + lmb_size = of_get_lmb_size(memory);
> +
> + /* Advance to the last cell, each cell has 6 32 bit integers */
> + dm += (drconf_cell_cnt - 1) * 6;
You could do this as follows to avoid hard-coding 6
dm += (drconf_cell_cnt - 1) * sizeof(struct of_drconf_cell)
> + read_drconf_cell(&drmem, &dm);
> + of_node_put(memory);
> + }
> + return drmem.base_addr + lmb_size;
I assume it is a safe assumption that there will only be 1 RMA LMB?
I do see that the PAPR defines a bit in the flags field for each LMB
in ibm,dynamic-memory as 'reserved'. Is this something you could use
to flag RMA LMBs and put them in the ibm,dynamic-memory property?
I'm just curious why these LMBs are not in this property.
-Nathan
> }
>
> /*
>
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