Patch "powerpc/pseries/ddw: Do not try direct mapping with persistent memory and one window" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    powerpc/pseries/ddw: Do not try direct mapping with persistent memory and one window

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     powerpc-pseries-ddw-do-not-try-direct-mapping-with-p.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 7aee3d2ccf3a363979c2845ddf05bf01ad4631e1
Author: Alexey Kardashevskiy <aik@xxxxxxxxx>
Date:   Mon Nov 8 15:03:19 2021 +1100

    powerpc/pseries/ddw: Do not try direct mapping with persistent memory and one window
    
    [ Upstream commit ad3976025b311cdeb822ad3e7a7554018cb0f83f ]
    
    There is a possibility of having just one DMA window available with
    a limited capacity which the existing code does not handle that well.
    If the window is big enough for the system RAM but less than
    MAX_PHYSMEM_BITS (which we want when persistent memory is present),
    we create 1:1 window and leave persistent memory without DMA.
    
    This disables 1:1 mapping entirely if there is persistent memory and
    either:
    - the huge DMA window does not cover the entire address space;
    - the default DMA window is removed.
    
    This relies on reverted 54fc3c681ded
    ("powerpc/pseries/ddw: Extend upper limit for huge DMA window for persistent memory")
    to return the actual amount RAM in ddw_memory_hotplug_max() (posted
    separately).
    
    Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx>
    Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20211108040320.3857636-4-aik@xxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
index ad96d6e13d1f6..8322ca86d5acf 100644
--- a/arch/powerpc/platforms/pseries/iommu.c
+++ b/arch/powerpc/platforms/pseries/iommu.c
@@ -1356,8 +1356,10 @@ static bool enable_ddw(struct pci_dev *dev, struct device_node *pdn)
 		len = order_base_2(query.largest_available_block << page_shift);
 		win_name = DMA64_PROPNAME;
 	} else {
-		direct_mapping = true;
-		win_name = DIRECT64_PROPNAME;
+		direct_mapping = !default_win_removed ||
+			(len == MAX_PHYSMEM_BITS) ||
+			(!pmem_present && (len == max_ram_len));
+		win_name = direct_mapping ? DIRECT64_PROPNAME : DMA64_PROPNAME;
 	}
 
 	ret = create_ddw(dev, ddw_avail, &create, page_shift, len);