linux-kernel - [PATCH AUTOSEL 5.15 04/39] powerpc/pseries/ddw: Do not try direct mapping with persistent memory and one window

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Date:   Thu, 25 Nov 2021 21:31:21 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Alexey Kardashevskiy <aik@...abs.ru>,
        Michael Ellerman <mpe@...erman.id.au>,
        Sasha Levin <sashal@...nel.org>, leobras.c@...il.com,
        fbarrat@...ux.ibm.com, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH AUTOSEL 5.15 04/39] powerpc/pseries/ddw: Do not try direct mapping with persistent memory and one window

From: Alexey Kardashevskiy <aik@...abs.ru>

[ 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@...abs.ru>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Link: https://lore.kernel.org/r/20211108040320.3857636-4-aik@ozlabs.ru
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/powerpc/platforms/pseries/iommu.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

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);
-- 
2.33.0