Hi, Dan > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Dan > Williams > Sent: Friday, December 9, 2016 10:05 AM > To: Zheng, Lv <[email protected]> > Cc: Rafael J. Wysocki <[email protected]>; Wysocki, Rafael J > <[email protected]>; Rafael J. > Wysocki <[email protected]>; Brown, Len <[email protected]>; Lv Zheng > <[email protected]>; Linux > Kernel Mailing List <[email protected]>; Linux ACPI > <[email protected]>; Moore, > Robert <[email protected]>; [email protected] > <[email protected]> > 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 5:59 PM, Zheng, Lv <[email protected]> wrote: > > Hi, Rafael and Dan > > > >> From: Dan Williams [mailto:[email protected]] > >> 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 <[email protected]> > >> wrote: > >> > On Thu, Dec 8, 2016 at 2:11 AM, Dan Williams <[email protected]> > >> > wrote: > >> >> On Tue, Nov 29, 2016 at 11:21 PM, Lv Zheng <[email protected]> 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 <[email protected]> > >> >>> Signed-off-by: Bob Moore <[email protected]> > >> >> > >> >> 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?
That should always be correct. In acpi_tb_init_table_descriptor(), table_desc->length is set by table_header->length. In acpi_tb_validate_table(), which calls acpi_tb_acquire_table(), acpi_os_map_memory() always uses table_desc->length. Thanks and best regards Lv > -- > To unsubscribe from this list: send the line "unsubscribe linux-acpi" in > the body of a message to [email protected] > More majordomo info at http://vger.kernel.org/majordomo-info.html
