I've not heard back, and I've got a conflict this afternoon. I'm going to resched for later in the week. Going to aim for Wednesday.
g.
On 02/09/2020 13:58, Grant Likely wrote:
On 02/09/2020 07:52, Ard Biesheuvel wrote:
On Wed, 2 Sep 2020 at 09:48, Heinrich Schuchardt xypron.glpk@gmx.de wrote:
On 9/1/20 10:51 AM, Ard Biesheuvel wrote:
On Tue, 1 Sep 2020 at 09:15, Heinrich Schuchardt xypron.glpk@gmx.de wrote:
On 8/31/20 9:01 PM, Ard Biesheuvel wrote:
On Mon, 31 Aug 2020 at 19:37, Heinrich Schuchardt xypron.glpk@gmx.de wrote: > > Closes: #52 > > The no-map property of the /reserved-memory DT node is used by > Linux to > signal that a memory region shall not be mapped and that > speculative access > shall not be permitted. > > The memory map returned by GetMemoryMap() does not have a flag > corresponding to no-map. So the closest thing we can do is not to > include > no-map reserved memory into the map returned by GetMemoryMap(). >
Dear Ard,
thanks for reviewing.
This violates the UEFI spec, which stipulates that the memory map describes all memory, no matter how it is used. It also interferes with the heuristics we use in Linux to decide which memory attributes to use when the code gets mapped explicitly (i.e., by a driver), which is permitted in the context of the /reserved-memory node (the no-map attribute applies to the linear map, but the region may still be mapped for other reasons). Note that an omitted region cannot carry EFI_MEMORY_WC/WT/WB attributes either.
Do you have an example of a no-map /reserved-memory node used in Linux?
Linux ignores DT provided memory reservations entirely when booting in UEFI mode, which is why it is important that the EFI memory map is synchronized. I am not aware of any examples.
Hello Ard,
I found the following compatibility strings for no-map areas in the Linux device trees:
compatible = "shared-dma-pool" compatible = "qcom,rmtfs-mem" compatible = "qcom,cmd-db"
If Linux simply ignores the no-map property from the device-tree when booting via UEFI and in UEFI we simply map those areas as reserved, there is a conceptual gap as you already stated in a separate mail.
There is definitely a gap, but reserved regions are already omitted from the linear map in Linux, so that is not a problem, i.e., the 'no-map' will be honoured as long as the firmware ensures that no-map regions are described as EfiReservedMemory.
In other words, today we just assume that the /reserved-memory node and the EFI memory map do not contradict each other, but we have no definition or explicit requirement anywhere what that actually means.
Yeah, we need to clean this up and make it consistent. Would like to have a call about this and look at some examples before trying to draft the requirement. We probably need something in either DT or EBBR that specifies exactly what is expected when using the UEFI boot path.
Does Monday 15:30BST work for a call?
g.
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