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:   Wed, 7 Dec 2016 17:11:14 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Lv Zheng <lv.zheng@...el.com>
Cc:     "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <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>,
        Bob Moore <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

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.

qemu=$HOME/git/qemu/build/x86_64-softmmu/qemu-system-x86_64
mem=$HOME/mem
label_size=$((128*1024))
mem_size=$(((3*1024*1024*1024) + (64 * 1024 *1024)))
IMAGE=$HOME/ahci.img

kvm=(
        $qemu
        -enable-kvm
        -cpu kvm64
        -kernel $kernel
        -initrd $initrd
        -m 12G,slots=3,maxmem=40G

        -machine pc-i440fx-2.4,accel=kvm,usb=off,vmport=off,nvdimm
        -cpu SandyBridge
        -smp 2
        -netdev tap,id=hostnet0,ifname=tap0,script=no,downscript=no
        -device
virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:b7:a1:ad,bus=pci.0,addr=0x7
        -object
memory-backend-file,id=mem1,share,mem-path=${mem},size=$((label_size +
mem_size))
        -device nvdimm,memdev=mem1,id=nv1,label-size=${label_size}
        -device ahci,id=sata0,bus=pci.0,addr=0x8
        -drive file=$IMAGE,if=none,id=drive-sata0-0-0,format=raw
        -device ide-hd,bus=sata0.0,drive=drive-sata0-0-0,id=sata0-0-0
        -boot order=nc
        -no-reboot
        -watchdog i6300esb
        -rtc base=localtime
        -serial stdio
        -display none
        -monitor null
)