On 15 March 2018 at 04:41, AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx> wrote: > On Wed, Mar 14, 2018 at 08:39:23AM +0000, Ard Biesheuvel wrote: >> On 14 March 2018 at 08:29, AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx> wrote: >> > In the last couples of months, there were some problems reported [1],[2] >> > around arm64 kexec/kdump. Where those phenomenon look different, >> > the root cause would be that kexec/kdump doesn't take into account >> > crucial "reserved" regions of system memory and unintentionally corrupts >> > them. >> > >> > Given that kexec-tools looks for all the information by seeking the file, >> > /proc/iomem, the first step to address said problems is to expand this file's >> > format so that it will have enough information about system memory and >> > its usage. >> > >> > Attached is my experimental code: With this patch applied, /proc/iomem sees >> > something like the below: >> > >> > (format A) >> > 40000000-5871ffff : System RAM >> > 40080000-40f1ffff : Kernel code >> > 41040000-411e8fff : Kernel data >> > 54400000-583fffff : Crash kernel >> > 58590000-585effff : EFI Resources >> > 58700000-5871ffff : EFI Resources >> > 58720000-58b5ffff : System RAM >> > 58720000-58b5ffff : EFI Resources >> > 58b60000-5be3ffff : System RAM >> > 58b61018-58b61947 : EFI Memory Map >> > 59a7b118-59a7b667 : EFI Configuration Tables >> > 5be40000-5becffff : System RAM <== (A-1) >> > 5be40000-5becffff : EFI Resources >> > 5bed0000-5bedffff : System RAM >> > 5bee0000-5bffffff : System RAM >> > 5bee0000-5bffffff : EFI Resources >> > 5c000000-5fffffff : System RAM >> > 8000000000-ffffffffff : PCI Bus 0000:00 >> > >> > Meanwhile, the workaround I suggested in [3] gave us a simpler view: >> > >> > (format B) >> > 40000000-5871ffff : System RAM >> > 40080000-40f1ffff : Kernel code >> > 41040000-411e9fff : Kernel data >> > 54400000-583fffff : Crash kernel >> > 58590000-585effff : reserved >> > 58700000-5871ffff : reserved >> > 58720000-58b5ffff : reserved >> > 58b60000-5be3ffff : System RAM >> > 58b61000-58b61fff : reserved >> > 59a7b318-59a7b867 : reserved >> > 5be40000-5becffff : reserved <== (B-1) >> > 5bed0000-5bedffff : System RAM >> > 5bee0000-5bffffff : reserved >> > 5c000000-5fffffff : System RAM >> > 5ec00000-5edfffff : reserved >> > 8000000000-ffffffffff : PCI Bus 0000:00 >> > >> > Here all the regions to be protected are named just "reserved" whether >> > they are NOMAP regions or simply-memblock_reserve'd. They are not very >> > useful for anything but kexec/kdump which knows what they mean. >> > >> > Alternatively, we may want to give them more specific names, based on >> > related efi memory map descriptors and else, that will characterize >> > their contents: >> > >> > (format C) >> > 40000000-5871ffff : System RAM >> > 40080000-40f1ffff : Kernel code >> > 41040000-411e9fff : Kernel data >> > 54400000-583fffff : Crash kernel >> > 58590000-585effff : ACPI Reclaim Memory >> > 58700000-5871ffff : ACPI Reclaim Memory >> > 58720000-58b5ffff : System RAM >> > 58720000-5878ffff : Runtime Data >> > 58790000-587dffff : Runtime Code >> > 587e0000-5882ffff : Runtime Data >> > 58830000-5887ffff : Runtime Code >> > 58880000-588cffff : Runtime Data >> > 588d0000-5891ffff : Runtime Code >> > 58920000-5896ffff : Runtime Data >> > 58970000-589bffff : Runtime Code >> > 589c0000-58a5ffff : Runtime Data >> > 58a60000-58abffff : Runtime Code >> > 58ac0000-58b0ffff : Runtime Data >> > 58b10000-58b5ffff : Runtime Code >> > 58b60000-5be3ffff : System RAM >> > 58b61000-58b61fff : EFI Memory Map >> > 59a7b118-59a7b667 : EFI Memory Attributes Table >> > 5be40000-5becffff : System RAM >> > 5be40000-5becffff : Runtime Code >> > 5bed0000-5bedffff : System RAM >> > 5bee0000-5bffffff : System RAM >> > 5bee0000-5bffffff : Runtime Data >> > 5c000000-5fffffff : System RAM >> > 8000000000-ffffffffff : PCI Bus 0000:00 >> > >> > I once created a patch for this format, but it looks quite noisy and >> > names are a sort of mixture of memory attributes( ACPI Reclaim memory, >> > Conventional Memory, Persistent Memory etc.) vs. >> > function/usages ([Loader|Boot Service|Runtime] Code/Data). >> > (As a matter of fact, (C-1) consists of various ACPI tables.) >> > Anyhow, they seem not so useful for most of other applications. >> > >> > Those observations lead to format A, where some entries with the same >> > attributes are squeezed into a single entry under a simple name if they >> > are neighbouring. >> > >> > >> > So my questions here are: >> > >> > 1. Which format, A, B, or C, is the most appropriate for the moment? >> > or any other suggestions? >> > >> >> I think some variant of B should be sufficient. The only meaningful >> distinction between these reserved regions at a general level is >> whether they are NOMAP or not, so perhaps we can incorporate that. > > I would definitely like to give your opinion the first priority, > but also hear from other guys. > > Can you tell my why you think that the distinction, NOMAP or not, > is meaningful? > For diagnostic purposes, it may be useful to know whether a certain address is covered by the linear mapping or not. >> As for identifying things like EFI configuration tables: this is a >> moving target, and we also define our own config tables for the TPM >> log, screeninfo on ARM etc. Also, for EFI memory types, you can boot >> with efi=debug and look at the entire memory map. So I think adding >> all that information may be overkill. > > No doubt I agree. > The reason why I gave specific names to EFI configuration tables > is that all such tables are unambiguously listed in 'efi' structure, > while "screen info" seems to be arm-specific. > As for EFI memory types, I admit that they are inadequate for a source > of naming. > Nevertheless, I still have a sense that "reserved" sounds sloppy :) > I don't think that sounds sloppy at all. >> > Currently, there is a inconsistent view between (A) and the mainline's: >> > see (A-1) and (B-1). If this is really a matter, I can fix it. >> > Kexec-tools can be easily modified to accept both formats, though. >> > >> > >> > 2. How should we determine which regions be exported in /proc/iomem? >> > >> > a. Trust all the memblock_reserve'd regions as my previous patch [3] does. >> > >> > As I said, it's a kind of "overkill." Some of regions, say fdt, are >> > not required to be preserved across kexec. >> > >> >> I don't think there is anything wrong with listing all >> memblock_reserve()'d regions here, even if kexec has other means of >> ensuring that they are not touched. > > I initially thought that one downside in this approach is that we might > not able to re-use a reserved region for fdt, as well as others also > dynamically reserved by "/reserved-memory/" nodes, after kexec and that > it would end up more or less a memory leak eventually after iterating > kexec()'s. But > after thinking twice, I now don't believe it is a problem anymore. > In kexec case, we won't have to hand over a list of reserved regions to > secondary kernel. Kdump, on the other hand, will be triggered only once > for its nature anyway. > >> But as I said, I think it would be >> useful to distinguish them from NOMAP regions (even if the nesting >> below System RAM already shows that as well) > > Something like "reserved (no map)"? > Works for me -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
