[PATCH 0/2] fdt: A couple of no-map fixes

In the context of a KVM/arm64 thread [1], it became apparent that the
difference in behaviour of EFI and DT with respect to no-map regions was
something worth fixing.

Rob pointed out in that thread that a couple of patches in this area had
been sent but still needed to be integrated together, which is basically
what this series attempts to do.

 - Patch 01 is a generic fix that should make sense on its own;

 - Patch 02 allows the kernel to have a saner behaviour with a broken DT.
   This one had a small rebase conflict (caused by patch 01). I tested
   it in qemu and everything is looking good, the error message shows up
   in dmesg when it should.

Thanks,
Quentin

[1] https://lore.kernel.org/kvmarm/20210108121524.656872-1-qperret@google.com/

KarimAllah Ahmed (1):
  fdt: Properly handle "no-map" field in the memory region

Nicolas Boichat (1):
  of/fdt: Make sure no-map does not remove already reserved regions

 drivers/of/fdt.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

-- 
2.30.0.284.gd98b1dd5eaa7-goog

From: KarimAllah Ahmed <redacted>

Mark the memory region with NOMAP flag instead of completely removing it
from the memory blocks. That makes the FDT handling consistent with the EFI
memory map handling.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Frank Rowand <redacted>
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: KarimAllah Ahmed <redacted>
Signed-off-by: Quentin Perret <redacted>
---
 drivers/of/fdt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index feb0f2d67fc5..427b534d60d2 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c

@@ -1147,7 +1147,7 @@ int __init __weak early_init_dt_reserve_memory_arch(phys_addr_t base,
 					phys_addr_t size, bool nomap)
 {
 	if (nomap)
-		return memblock_remove(base, size);
+		return memblock_mark_nomap(base, size);
 	return memblock_reserve(base, size);
 }
 

-- 
2.30.0.284.gd98b1dd5eaa7-goog

From: Nicolas Boichat <redacted>

If the device tree is incorrectly configured, and attempts to
define a "no-map" reserved memory that overlaps with the kernel
data/code, the kernel would crash quickly after boot, with no
obvious clue about the nature of the issue.

For example, this would happen if we have the kernel mapped at
these addresses (from /proc/iomem):
40000000-41ffffff : System RAM
  40080000-40dfffff : Kernel code
  40e00000-411fffff : reserved
  41200000-413e0fff : Kernel data

And we declare a no-map shared-dma-pool region at a fixed address
within that range:
mem_reserved: mem_region {
	compatible = "shared-dma-pool";
	reg = <0 0x40000000 0 0x01A00000>;
	no-map;
};

To fix this, when removing memory regions at early boot (which is
what "no-map" regions do), we need to make sure that the memory
is not already reserved. If we do, __reserved_mem_reserve_reg
will throw an error:
[    0.000000] OF: fdt: Reserved memory: failed to reserve memory
   for node 'mem_region': base 0x0000000040000000, size 26 MiB
and the code that will try to use the region should also fail,
later on.

We do not do anything for non-"no-map" regions, as memblock
explicitly allows reserved regions to overlap, and the commit
that this fixes removed the check for that precise reason.

[ qperret: fixed conflicts caused by the usage of memblock_mark_nomap ]

Fixes: 094cb98179f19b7 ("of/fdt: memblock_reserve /memreserve/ regions in the case of partial overlap")
Signed-off-by: Nicolas Boichat <redacted>
Reviewed-by: Stephen Boyd <redacted>
Signed-off-by: Quentin Perret <redacted>
---
 drivers/of/fdt.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index 427b534d60d2..dcc1dd96911a 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c

@@ -1146,8 +1146,16 @@ int __init __weak early_init_dt_mark_hotplug_memory_arch(u64 base, u64 size)
 int __init __weak early_init_dt_reserve_memory_arch(phys_addr_t base,
 					phys_addr_t size, bool nomap)
 {
-	if (nomap)
+	if (nomap) {
+		/*
+		 * If the memory is already reserved (by another region), we
+		 * should not allow it to be marked nomap.
+		 */
+		if (memblock_is_region_reserved(base, size))
+			return -EBUSY;
+
 		return memblock_mark_nomap(base, size);
+	}
 	return memblock_reserve(base, size);
 }
 

-- 
2.30.0.284.gd98b1dd5eaa7-goog

On Fri, 15 Jan 2021 11:45:43 +0000, Quentin Perret wrote:

From: KarimAllah Ahmed <redacted>

Mark the memory region with NOMAP flag instead of completely removing it
from the memory blocks. That makes the FDT handling consistent with the EFI
memory map handling.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Frank Rowand <redacted>
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: KarimAllah Ahmed <redacted>
Signed-off-by: Quentin Perret <redacted>
---
 drivers/of/fdt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Applied, thanks!

On Fri, 15 Jan 2021 11:45:44 +0000, Quentin Perret wrote:

From: Nicolas Boichat <redacted>

If the device tree is incorrectly configured, and attempts to
define a "no-map" reserved memory that overlaps with the kernel
data/code, the kernel would crash quickly after boot, with no
obvious clue about the nature of the issue.

For example, this would happen if we have the kernel mapped at
these addresses (from /proc/iomem):
40000000-41ffffff : System RAM
  40080000-40dfffff : Kernel code
  40e00000-411fffff : reserved
  41200000-413e0fff : Kernel data

And we declare a no-map shared-dma-pool region at a fixed address
within that range:
mem_reserved: mem_region {
	compatible = "shared-dma-pool";
	reg = <0 0x40000000 0 0x01A00000>;
	no-map;
};

To fix this, when removing memory regions at early boot (which is
what "no-map" regions do), we need to make sure that the memory
is not already reserved. If we do, __reserved_mem_reserve_reg
will throw an error:
[    0.000000] OF: fdt: Reserved memory: failed to reserve memory
   for node 'mem_region': base 0x0000000040000000, size 26 MiB
and the code that will try to use the region should also fail,
later on.

We do not do anything for non-"no-map" regions, as memblock
explicitly allows reserved regions to overlap, and the commit
that this fixes removed the check for that precise reason.

[ qperret: fixed conflicts caused by the usage of memblock_mark_nomap ]

Fixes: 094cb98179f19b7 ("of/fdt: memblock_reserve /memreserve/ regions in the case of partial overlap")
Signed-off-by: Nicolas Boichat <redacted>
Reviewed-by: Stephen Boyd <redacted>
Signed-off-by: Quentin Perret <redacted>
---
 drivers/of/fdt.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

Applied, thanks!

On Sat, Jan 16, 2021 at 1:30 AM Rob Herring [off-list ref] wrote:

On Fri, 15 Jan 2021 11:45:44 +0000, Quentin Perret wrote:

quoted

From: Nicolas Boichat <redacted>

If the device tree is incorrectly configured, and attempts to
define a "no-map" reserved memory that overlaps with the kernel
data/code, the kernel would crash quickly after boot, with no
obvious clue about the nature of the issue.

For example, this would happen if we have the kernel mapped at
these addresses (from /proc/iomem):
40000000-41ffffff : System RAM
  40080000-40dfffff : Kernel code
  40e00000-411fffff : reserved
  41200000-413e0fff : Kernel data

And we declare a no-map shared-dma-pool region at a fixed address
within that range:
mem_reserved: mem_region {
      compatible = "shared-dma-pool";
      reg = <0 0x40000000 0 0x01A00000>;
      no-map;
};

To fix this, when removing memory regions at early boot (which is
what "no-map" regions do), we need to make sure that the memory
is not already reserved. If we do, __reserved_mem_reserve_reg
will throw an error:
[    0.000000] OF: fdt: Reserved memory: failed to reserve memory
   for node 'mem_region': base 0x0000000040000000, size 26 MiB
and the code that will try to use the region should also fail,
later on.

We do not do anything for non-"no-map" regions, as memblock
explicitly allows reserved regions to overlap, and the commit
that this fixes removed the check for that precise reason.

[ qperret: fixed conflicts caused by the usage of memblock_mark_nomap ]

Fixes: 094cb98179f19b7 ("of/fdt: memblock_reserve /memreserve/ regions in the case of partial overlap")
Signed-off-by: Nicolas Boichat <redacted>
Reviewed-by: Stephen Boyd <redacted>
Signed-off-by: Quentin Perret <redacted>
---
 drivers/of/fdt.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

Thanks for picking up this old patch Quentin ,-)

Applied, thanks!