linux-kernel - RE: [PATCH 08/11] ACPICA: Tables: Back port acpi_get_table_with_size() and early_acpi_os_unmap

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Date:   Fri, 9 Dec 2016 01:59:34 +0000
From:   "Zheng, Lv" <lv.zheng@...el.com>
To:     "Williams, Dan J" <dan.j.williams@...el.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>
CC:     "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "Brown, Len" <len.brown@...el.com>, Lv Zheng <zetalog@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        "Moore, Robert" <robert.moore@...el.com>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...1.01.org>
Subject: RE: [PATCH 08/11] ACPICA: Tables: Back port
 acpi_get_table_with_size() and early_acpi_os_unmap_memory() from Linux kernel

Hi, Rafael and Dan

> From: Dan Williams [mailto:dan.j.williams@...el.com]
> 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@...nel.org> wrote:
> > On Thu, Dec 8, 2016 at 2:11 AM, Dan Williams <dan.j.williams@...el.com> wrote:
> >> On Tue, Nov 29, 2016 at 11:21 PM, Lv Zheng <lv.zheng@...el.com> 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@...el.com>
> >>> Signed-off-by: Bob Moore <robert.moore@...el.com>
> >>
> >> 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.

To Rafael:
I can offer a quick fix for this by returning table_header->length from acpi_get_table_with_size().

Thanks and best regards
Lv