On Thu, Dec 8, 2016 at 5:59 PM, Zheng, Lv <lv.zheng@xxxxxxxxx> wrote: > Hi, Rafael and Dan > >> From: Dan Williams [mailto:dan.j.williams@xxxxxxxxx] >> Subject: Re: [PATCH 08/11] ACPICA: Tables: Back port acpi_get_table_with_size() and >> early_acpi_os_unmap_memory() from Linux kernel >> >> On Thu, Dec 8, 2016 at 5:18 AM, Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote: >> > On Thu, Dec 8, 2016 at 2:11 AM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote: >> >> On Tue, Nov 29, 2016 at 11:21 PM, Lv Zheng <lv.zheng@xxxxxxxxx> wrote: >> >>> ACPICA commit cac6790954d4d752a083e6122220b8a22febcd07 >> >>> >> >>> This patch back ports Linux acpi_get_table_with_size() and >> >>> early_acpi_os_unmap_memory() into ACPICA upstream to reduce divergences. >> >>> >> >>> The 2 APIs are used by Linux as table management APIs for long time, it >> >>> contains a hidden logic that during the early stage, the mapped tables >> >>> should be unmapped before the early stage ends. >> >>> >> >>> During the early stage, tables are handled by the following sequence: >> >>> acpi_get_table_with_size(); >> >>> parse the table >> >>> early_acpi_os_unmap_memory(); >> >>> During the late stage, tables are handled by the following sequence: >> >>> acpi_get_table(); >> >>> parse the table >> >>> Linux uses acpi_gbl_permanent_mmap to distinguish the early stage and the >> >>> late stage. >> >>> >> >>> The reasoning of introducing acpi_get_table_with_size() is: ACPICA will >> >>> remember the early mapped pointer in acpi_get_table() and Linux isn't able to >> >>> prevent ACPICA from using the wrong early mapped pointer during the late >> >>> stage as there is no API provided from ACPICA to be an inverse of >> >>> acpi_get_table() to forget the early mapped pointer. >> >>> >> >>> But how ACPICA can work with the early/late stage requirement? Inside of >> >>> ACPICA, tables are ensured to be remained in "INSTALLED" state during the >> >>> early stage, and they are carefully not transitioned to "VALIDATED" state >> >>> until the late stage. So the same logic is in fact implemented inside of >> >>> ACPICA in a different way. The gap is only that the feature is not provided >> >>> to the OSPMs in an accessible external API style. >> >>> >> >>> It then is possible to fix the gap by providing an inverse of >> >>> acpi_get_table() from ACPICA, so that the two Linux sequences can be >> >>> combined: >> >>> acpi_get_table(); >> >>> parse the table >> >>> acpi_put_table(); >> >>> In order to work easier with the current Linux code, acpi_get_table() and >> >>> acpi_put_table() is implemented in a usage counting based style: >> >>> 1. When the usage count of the table is increased from 0 to 1, table is >> >>> mapped and .Pointer is set with the mapping address (VALIDATED); >> >>> 2. When the usage count of the table is decreased from 1 to 0, .Pointer >> >>> is unset and the mapping address is unmapped (INVALIDATED). >> >>> So that we can deploy the new APIs to Linux with minimal effort by just >> >>> invoking acpi_get_table() in acpi_get_table_with_size() and invoking >> >>> acpi_put_table() in early_acpi_os_unmap_memory(). Lv Zheng. >> >>> >> >>> Link: https://github.com/acpica/acpica/commit/cac67909 >> >>> Signed-off-by: Lv Zheng <lv.zheng@xxxxxxxxx> >> >>> Signed-off-by: Bob Moore <robert.moore@xxxxxxxxx> >> >> >> >> This commit in -next (071b39575679 ACPICA: Tables: Back port >> >> acpi_get_table_with_size() and early_acpi_os_unmap_memory() from Linux >> >> kernel) causes a regression in my nfit/nvdimm test environment. The >> >> nfit produced by QEMU no longer results in a nvdimm bus being created. >> >> >> >> I have not root caused it, but I'm using the following command line >> >> options to create an nfit in qemu-2.6. Reverting the commit leads >> >> compile failures. >> > >> > Would the build problems go away if you reverted "ACPICA: Tables: >> > Allow FADT to be customized with virtual address" (linux-next commit >> > cf334d3174f9) in addition to it? >> >> Yes, reverting those two commits gets me back to a functional environment: >> >> Revert "ACPICA: Tables: Allow FADT to be customized with virtual address" >> Revert "ACPICA: Tables: Back port acpi_get_table_with_size() and >> early_acpi_os_un > > To Dan: > It seems in drivers/acpi/nfit/core.c. > The returned table size is used by the NFIT code. > I think it should be changed to use table_header->length. Does the acpi core already validate that table_header->length is correct? i.e. is is possible that a broken implementation could have the wrong length in the header? I was assuming that was the purpose of the _with_size(), but maybe I was wrong? -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
