Date:   Fri, 9 Dec 2016 01:49:45 +0000
From:   "Zheng, Lv" <lv.zheng@...el.com>
To:     "Williams, Dan J" <dan.j.williams@...el.com>
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, Dan

Good to see you here!

> From: dan.j.williams@...il.com [mailto:dan.j.williams@...il.com] On Behalf Of Dan Williams
> 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.

This commit is almost a no-op, unless some code in kernel is using the length field returned by old acpi_get_table_with_size().

> 
> 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
> )

Let me file a kernel Bugzilla bug to track this issue:
https://bugzilla.kernel.org/show_bug.cgi?id=189891
And see if we can quickly fix it.

Could you also point me the NFIT code that I should take a look at.
Thanks in advance.

Best regards
Lv

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