On Tue, Mar 02, 2021 at 07:43:40PM +0100, David Hildenbrand wrote: > > > > The resizeable memory region that is created for the cmd blob has a > > > > maximum > > > > size of ACPI_BUILD_ALIGN_SIZE - 4k. This used to be sufficient, however, > > > > The expression "ACPI_BUILD_ALIGN_SIZE - 4k" makes no sense to me. > > ACPI_BUILD_ALIGN_SIZE is #defined in "hw/i386/acpi-build.c" as 0x1000, > > so the difference (ACPI_BUILD_ALIGN_SIZE - 4k) is zero. > > > > (1) Did you mean "ACPI_BUILD_ALIGN_SIZE -- 4k"? IOW, did you mean to > > quote the value of the macro? > > > > If you mean an em dash, then please use an em dash, not a hyphen (or > > please use parens). > > Yes, or rather use ACPI_BUILD_ALIGN_SIZE (4k). > > > > > > > > > as we try fitting in additional data (e.g., vmgenid, nvdimm, > > > > intel-iommu), > > > > we require more than 4k and can crash QEMU when trying to resize the > > > > resizeable memory region beyond its maximum size: > > > > $ build/qemu-system-x86_64 --enable-kvm \ > > > > -machine q35,nvdimm=on \ > > > > -smp 1 \ > > > > -cpu host \ > > > > -m size=2G,slots=8,maxmem=4G \ > > > > -object > > > > memory-backend-file,id=mem0,mem-path=/tmp/nvdimm,size=256M \ > > > > -device nvdimm,label-size=131072,memdev=mem0,id=nvdimm0,slot=1 \ > > > > -nodefaults \ > > > > -device vmgenid \ > > > > -device intel-iommu > > > > > > > > Results in: > > > > Unexpected error in qemu_ram_resize() at ../softmmu/physmem.c:1850: > > > > qemu-system-x86_64: Size too large: /rom@etc/table-loader: > > > > 0x2000 > 0x1000: Invalid argument > > > > > > > > We try growing the resizeable memory region (resizeable RAMBlock) beyond > > > > its maximum size. Let's increase the maximum size from 4k to 64k, which > > > > should be good enough for the near future. > > > > The existent code calls acpi_align_size(), for resizing the ACPI blobs > > (the GArray objects). > > > > (Unfortunately, the acpi_align_size() function is duplicated between > > "hw/i386/acpi-build.c" and "hw/arm/virt-acpi-build.c", which seems > > unjustified -- but anyway, I digress.) > > > > This seems to come from commit 868270f23d8d ("acpi-build: tweak acpi > > migration limits", 2014-07-29) and commit 451b157041d2 ("acpi: Align the > > size to 128k", 2020-12-08). > > > > (2) Why is the logic added in those commits insufficient? > > We are dealing with different blobs here (tables_blob vs. cmd_blob). > > > > > What is the exact call tree that triggers the above error? > > [...] > > acpi_build_update()->acpi_build_update()->memory_region_ram_resize()->qemu_ram_resize() > > A longer calltrace can be found in > https://bugzilla.redhat.com/show_bug.cgi?id=1927159. > > > > > +++ b/hw/i386/acpi-microvm.c > > > > @@ -255,7 +255,8 @@ void acpi_setup_microvm(MicrovmMachineState *mms) > > > > ACPI_BUILD_TABLE_MAX_SIZE); > > > > acpi_add_rom_blob(acpi_build_no_update, NULL, > > > > tables.linker->cmd_blob, > > > > - "etc/table-loader", 0); > > > > + ACPI_BUILD_LOADER_FILE, > > > > + ACPI_BUILD_LOADER_MAX_SIZE); > > > > acpi_add_rom_blob(acpi_build_no_update, NULL, > > > > tables.rsdp, > > > > ACPI_BUILD_RSDP_FILE, 0); > > > > (3) Why are we using a different "tool" here, from the previous > > approach? We're no longer setting the GArray sizes; instead, we make the > > "rom->romsize" fields diverge from -- put differently, grow beyond -- > > "rom->datasize". Why is that useful? What are the consequences? > > See ACPI_BUILD_TABLE_MAX_SIZE handling just in the acpi_add_rom_blob() above. > > > > > Where is it ensured that data between "rom->datasize" and "rom->romsize" > > reads as zeroes? > We only expose the current memory_region_size() to our guest, which is > always multiples of 4k pages. > > rom->datasize and rom->romsize will be multiple of 4k AFAIKs. > > acpi_align_size()-> g_array_set_size() will take care of zeroing out > any unused parts within a single 4k page. > > So all unused, guest-visible part should always be 0 I think. > > > > > > > > > diff --git a/include/hw/acpi/aml-build.h b/include/hw/acpi/aml-build.h > > > > index 380d3e3924..93cdfd4006 100644 > > > > --- a/include/hw/acpi/aml-build.h > > > > +++ b/include/hw/acpi/aml-build.h > > > > @@ -6,6 +6,7 @@ > > > > > > > > /* Reserve RAM space for tables: add another order of magnitude. */ > > > > #define ACPI_BUILD_TABLE_MAX_SIZE 0x200000 > > > > +#define ACPI_BUILD_LOADER_MAX_SIZE 0x40000 > > > > > > > > #define ACPI_BUILD_APPNAME6 "BOCHS " > > > > #define ACPI_BUILD_APPNAME8 "BXPC " > > > > > > > The commit message says "Let's increase the maximum size from 4k to > > 64k", and I have two problems with that: > > > > (4a) I have no idea where the current "4k" size comes from. (In case the > > 4k refers to ACPI_BUILD_ALIGN_SIZE, then why are we not changing that > > macro?) > > Changing ACPI_BUILD_ALIGN_SIZE would affect the legacy_table_size in > acpi_build() - so that can't be right. > > What would also work is something like (to be improved) > > diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c > index 45ad2f9533..49cfedddc8 100644 > --- a/hw/i386/acpi-build.c > +++ b/hw/i386/acpi-build.c > @@ -81,6 +81,8 @@ > #define ACPI_BUILD_LEGACY_CPU_AML_SIZE 97 > #define ACPI_BUILD_ALIGN_SIZE 0x1000 > +#define ACPI_BUILD_LOADER_ALIGN_SIZE 0x2000 > + > #define ACPI_BUILD_TABLE_SIZE 0x20000 > /* #define DEBUG_ACPI_BUILD */ > @@ -2613,10 +2615,10 @@ void acpi_build(AcpiBuildTables *tables, MachineState > *machine) > error_printf("Try removing CPUs, NUMA nodes, memory slots" > " or PCI bridges."); > } > - acpi_align_size(tables_blob, ACPI_BUILD_TABLE_SIZE); > + acpi_align_size(tables_blob, ACPI_BUILD_ALIGN_SIZE); > } > - acpi_align_size(tables->linker->cmd_blob, ACPI_BUILD_ALIGN_SIZE); > + acpi_align_size(tables->linker->cmd_blob, ACPI_BUILD_LOADER_ALIGN_SIZE); > > > At least for hw/i386/acpi-build.c. > > We will end up creating the resizeable memory region/RAMBlock always with > a size=maximum_size=8k. (could also go for 64k here) > > The only downside is that we might expose a bigger area to the > guest than necessary (e.g., 8k instead of 4k) and will e.g., migrate > 8k instead of 4k (not that we care). > > > On incoming migration from older QEMU versions, we should be able to just > shrink back from 8k to 4k - so migration from older QEMY versions should > continue working just fine.
what about migration to old qemu? > > > > (4b) The new macro ACPI_BUILD_LOADER_MAX_SIZE does not express 64KB, > > contrary to the commit message: it expresses 256KB. > > Indeed, thanks for noticing that - not that it wouldn't really > affect your testing in case the maximum size is bigger than necessary ;) > > > > > ... The code is really difficult to understand; consider the following > > macros: > > Yes, it is. > > Thanks! > > -- > Thanks, > > David / dhildenb