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Re: [PATCH for-4.14 2/3] xen/arm: Take into account the DMA width when allocating Dom0 memory banks

On 18/05/2020 21:34, Volodymyr Babchuk wrote:
Hi Julien,

Hi Volodymyr,

Thank you for the review.

On Mon, 2020-05-18 at 12:30 +0100, Julien Grall wrote:
From: Julien Grall <jgrall@xxxxxxxxxx>

At the moment, Xen is assuming that all the devices are at least 32-bit
DMA capable. However, some SoCs have devices that may be able to access
a much restricted range. For instance, the Raspberry PI 4 has devices
that can only access the first GB of RAM.

The function arch_get_dma_bit_size() will return the lowest DMA width on
the platform. Use it to decide what is the limit for the low memory.

Signed-off-by: Julien GralL <jgrall@xxxxxxxxxx>
  xen/arch/arm/domain_build.c | 32 +++++++++++++++++++-------------
  1 file changed, 19 insertions(+), 13 deletions(-)

diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 430708753642..abc4e463d27c 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -211,10 +211,13 @@ fail:
   *    the ramdisk and DTB must be placed within a certain proximity of
   *    the kernel within RAM.
   * 3. For dom0 we want to place as much of the RAM as we reasonably can
- *    below 4GB, so that it can be used by non-LPAE enabled kernels (32-bit)
+ *    below 4GB, so that it can be used by non-LPAE enabled kernels (32-bit).
Is full stop really needed there?

I was meant to remove the line below as it is now part of 4). I will remove it in the next version.

Best regards,

Julien Grall



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