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David Hildenbrand

2020-Apr-30 07:19 UTC

[PATCH v1 2/3] mm/memory_hotplug: Introduce MHP_DRIVER_MANAGED

On 29.04.20 18:08, David Hildenbrand wrote:> Some paravirtualized devices that add memory via add_memory() and
> friends (esp. virtio-mem) don't want to create entries in
> /sys/firmware/memmap/ - primarily to hinder kexec from adding this
> memory to the boot memmap of the kexec kernel.
> 
> In fact, such memory is never exposed via the firmware (e.g., e820), but
> only via the device, so exposing this memory via /sys/firmware/memmap/ is
> wrong:
>  "kexec needs the raw firmware-provided memory map to setup the
>   parameter segment of the kernel that should be booted with
>   kexec. Also, the raw memory map is useful for debugging. For
>   that reason, /sys/firmware/memmap is an interface that provides
>   the raw memory map to userspace." [1]
> 
> We want to let user space know that memory which is always detected,
> added, and managed via a (device) driver - like memory managed by
> virtio-mem - is special. It cannot be used for placing kexec segments
> and the (device) driver is responsible for re-adding memory that
> (eventually shrunk/grown/defragmented) memory after a reboot/kexec. It
> should e.g., not be added to a fixed up firmware memmap. However, it should
> be dumped by kdump.
> 
> Also, such memory could behave differently than an ordinary DIMM - e.g.,
> memory managed by virtio-mem can have holes inside added memory resource,
> which should not be touched, especially for writing.
> 
> Let's expose that memory as "System RAM (driver managed)"
e.g., via
> /pro/iomem.
> 
> We don't have to worry about firmware_map_remove() on the removal path.
> If there is no entry, it will simply return with -EINVAL.
> 
> [1]
https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-firmware-memmap
> 
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Cc: Michal Hocko <mhocko at suse.com>
> Cc: Pankaj Gupta <pankaj.gupta.linux at gmail.com>
> Cc: Wei Yang <richard.weiyang at gmail.com>
> Cc: Baoquan He <bhe at redhat.com>
> Cc: Eric Biederman <ebiederm at xmission.com>
> Signed-off-by: David Hildenbrand <david at redhat.com>
> ---
>  include/linux/memory_hotplug.h |  8 ++++++++
>  mm/memory_hotplug.c            | 20 ++++++++++++++++----
>  2 files changed, 24 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/memory_hotplug.h
b/include/linux/memory_hotplug.h
> index bf0e3edb8688..cc538584b39e 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -68,6 +68,14 @@ struct mhp_params {
>  	pgprot_t pgprot;
>  };
>  
> +/* Flags used for add_memory() and friends. */
> +
> +/*
> + * Don't create entries in /sys/firmware/memmap/ and expose memory as
> + * "System RAM (driver managed)" in e.g., /proc/iomem
> + */
> +#define MHP_DRIVER_MANAGED		1
> +
>  /*
>   * Zone resizing functions
>   *
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index ebdf6541d074..cfa0721280aa 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -98,11 +98,11 @@ void mem_hotplug_done(void)
>  u64 max_mem_size = U64_MAX;
>  
>  /* add this memory to iomem resource */
> -static struct resource *register_memory_resource(u64 start, u64 size)
> +static struct resource *register_memory_resource(u64 start, u64 size,
> +						 const char *resource_name)
>  {
>  	struct resource *res;
>  	unsigned long flags =  IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
> -	char *resource_name = "System RAM";
>  
>  	/*
>  	 * Make sure value parsed from 'mem=' only restricts memory
adding
> @@ -1058,7 +1058,8 @@ int __ref add_memory_resource(int nid, struct
resource *res,
>  	BUG_ON(ret);
>  
>  	/* create new memmap entry */
> -	firmware_map_add_hotplug(start, start + size, "System RAM");
> +	if (!(flags & MHP_DRIVER_MANAGED))
> +		firmware_map_add_hotplug(start, start + size, "System RAM");
>  
>  	/* device_online() will take the lock when calling online_pages() */
>  	mem_hotplug_done();
> @@ -1081,10 +1082,21 @@ int __ref add_memory_resource(int nid, struct
resource *res,
>  /* requires device_hotplug_lock, see add_memory_resource() */
>  int __ref __add_memory(int nid, u64 start, u64 size, unsigned long flags)
>  {
> +	const char *resource_name = "System RAM";
>  	struct resource *res;
>  	int ret;
>  
> -	res = register_memory_resource(start, size);
> +	/*
> +	 * Indicate that memory managed by a driver is special. It's always
> +	 * detected and added via a driver, should not be given to the kexec
> +	 * kernel for booting when manually crafting the firmware memmap, and
> +	 * no kexec segments should be placed on it. However, kdump should
> +	 * dump this memory.
> +	 */
> +	if (flags & MHP_DRIVER_MANAGED)
> +		resource_name = "System RAM (driver managed)";
> +
> +	res = register_memory_resource(start, size, resource_name);
>  	if (IS_ERR(res))
>  		return PTR_ERR(res);
>  
> 
BTW, I was wondering if this is actually also something that
drivers/dax/kmem.c wants to use for adding memory.

Just because we decided to use some DAX memory in the current kernel as
system ram, doesn't mean we should make that decision for the kexec
kernel (e.g., using it as initial memory, placing kexec binaries onto
it, etc.). This is also not what we would observe during a real reboot.

I can see that the "System RAM" resource will show up as child
resource
under the device e.g., in /proc/iomem.

However, entries in /sys/firmware/memmap/ are created as "System RAM".

-- 
Thanks,

David / dhildenb

Dan Williams

2020-Apr-30 08:11 UTC

head link

[PATCH v1 2/3] mm/memory_hotplug: Introduce MHP_DRIVER_MANAGED

On Thu, Apr 30, 2020 at 12:20 AM David Hildenbrand <david at redhat.com>
wrote:>
> On 29.04.20 18:08, David Hildenbrand wrote:
> > Some paravirtualized devices that add memory via add_memory() and
> > friends (esp. virtio-mem) don't want to create entries in
> > /sys/firmware/memmap/ - primarily to hinder kexec from adding this
> > memory to the boot memmap of the kexec kernel.
> >
> > In fact, such memory is never exposed via the firmware (e.g., e820),
but
> > only via the device, so exposing this memory via /sys/firmware/memmap/
is
> > wrong:
> >  "kexec needs the raw firmware-provided memory map to setup the
> >   parameter segment of the kernel that should be booted with
> >   kexec. Also, the raw memory map is useful for debugging. For
> >   that reason, /sys/firmware/memmap is an interface that provides
> >   the raw memory map to userspace." [1]
> >
> > We want to let user space know that memory which is always detected,
> > added, and managed via a (device) driver - like memory managed by
> > virtio-mem - is special. It cannot be used for placing kexec segments
> > and the (device) driver is responsible for re-adding memory that
> > (eventually shrunk/grown/defragmented) memory after a reboot/kexec. It
> > should e.g., not be added to a fixed up firmware memmap. However, it
should
> > be dumped by kdump.
> >
> > Also, such memory could behave differently than an ordinary DIMM -
e.g.,
> > memory managed by virtio-mem can have holes inside added memory
resource,
> > which should not be touched, especially for writing.
> >
> > Let's expose that memory as "System RAM (driver
managed)" e.g., via
> > /pro/iomem.
> >
> > We don't have to worry about firmware_map_remove() on the removal
path.
> > If there is no entry, it will simply return with -EINVAL.
> >
> > [1]
https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-firmware-memmap
> >
> > Cc: Andrew Morton <akpm at linux-foundation.org>
> > Cc: Michal Hocko <mhocko at suse.com>
> > Cc: Pankaj Gupta <pankaj.gupta.linux at gmail.com>
> > Cc: Wei Yang <richard.weiyang at gmail.com>
> > Cc: Baoquan He <bhe at redhat.com>
> > Cc: Eric Biederman <ebiederm at xmission.com>
> > Signed-off-by: David Hildenbrand <david at redhat.com>
> > ---
> >  include/linux/memory_hotplug.h |  8 ++++++++
> >  mm/memory_hotplug.c            | 20 ++++++++++++++++----
> >  2 files changed, 24 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/linux/memory_hotplug.h
b/include/linux/memory_hotplug.h
> > index bf0e3edb8688..cc538584b39e 100644
> > --- a/include/linux/memory_hotplug.h
> > +++ b/include/linux/memory_hotplug.h
> > @@ -68,6 +68,14 @@ struct mhp_params {
> >       pgprot_t pgprot;
> >  };
> >
> > +/* Flags used for add_memory() and friends. */
> > +
> > +/*
> > + * Don't create entries in /sys/firmware/memmap/ and expose
memory as
> > + * "System RAM (driver managed)" in e.g., /proc/iomem
> > + */
> > +#define MHP_DRIVER_MANAGED           1
> > +
> >  /*
> >   * Zone resizing functions
> >   *
> > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > index ebdf6541d074..cfa0721280aa 100644
> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> > @@ -98,11 +98,11 @@ void mem_hotplug_done(void)
> >  u64 max_mem_size = U64_MAX;
> >
> >  /* add this memory to iomem resource */
> > -static struct resource *register_memory_resource(u64 start, u64 size)
> > +static struct resource *register_memory_resource(u64 start, u64 size,
> > +                                              const char
*resource_name)
> >  {
> >       struct resource *res;
> >       unsigned long flags =  IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
> > -     char *resource_name = "System RAM";
> >
> >       /*
> >        * Make sure value parsed from 'mem=' only restricts
memory adding
> > @@ -1058,7 +1058,8 @@ int __ref add_memory_resource(int nid, struct
resource *res,
> >       BUG_ON(ret);
> >
> >       /* create new memmap entry */
> > -     firmware_map_add_hotplug(start, start + size, "System
RAM");
> > +     if (!(flags & MHP_DRIVER_MANAGED))
> > +             firmware_map_add_hotplug(start, start + size,
"System RAM");
> >
> >       /* device_online() will take the lock when calling
online_pages() */
> >       mem_hotplug_done();
> > @@ -1081,10 +1082,21 @@ int __ref add_memory_resource(int nid, struct
resource *res,
> >  /* requires device_hotplug_lock, see add_memory_resource() */
> >  int __ref __add_memory(int nid, u64 start, u64 size, unsigned long
flags)
> >  {
> > +     const char *resource_name = "System RAM";
> >       struct resource *res;
> >       int ret;
> >
> > -     res = register_memory_resource(start, size);
> > +     /*
> > +      * Indicate that memory managed by a driver is special. It's
always
> > +      * detected and added via a driver, should not be given to the
kexec
> > +      * kernel for booting when manually crafting the firmware
memmap, and
> > +      * no kexec segments should be placed on it. However, kdump
should
> > +      * dump this memory.
> > +      */
> > +     if (flags & MHP_DRIVER_MANAGED)
> > +             resource_name = "System RAM (driver managed)";
> > +
> > +     res = register_memory_resource(start, size, resource_name);
> >       if (IS_ERR(res))
> >               return PTR_ERR(res);
> >
> >
>
> BTW, I was wondering if this is actually also something that
> drivers/dax/kmem.c wants to use for adding memory.
>
> Just because we decided to use some DAX memory in the current kernel as
> system ram, doesn't mean we should make that decision for the kexec
> kernel (e.g., using it as initial memory, placing kexec binaries onto
> it, etc.). This is also not what we would observe during a real reboot.
Agree.
> I can see that the "System RAM" resource will show up as child
resource
> under the device e.g., in /proc/iomem.
>
> However, entries in /sys/firmware/memmap/ are created as "System
RAM".
True. Do you think this rename should just be limited to what type
/sys/firmware/memmap/ emits? I have the concern, but no proof
currently, that there are /proc/iomem walkers that explicitly look for
"System RAM", but might be thrown off by "System RAM (driver
managed)". I was not aware of /sys/firmware/memmap until about 5
minutes ago.

David Hildenbrand

2020-Apr-30 08:20 UTC

head link

[PATCH v1 2/3] mm/memory_hotplug: Introduce MHP_DRIVER_MANAGED

On 30.04.20 10:11, Dan Williams wrote:> On Thu, Apr 30, 2020 at 12:20 AM David Hildenbrand <david at
redhat.com> wrote:
>>
>> On 29.04.20 18:08, David Hildenbrand wrote:
>>> Some paravirtualized devices that add memory via add_memory() and
>>> friends (esp. virtio-mem) don't want to create entries in
>>> /sys/firmware/memmap/ - primarily to hinder kexec from adding this
>>> memory to the boot memmap of the kexec kernel.
>>>
>>> In fact, such memory is never exposed via the firmware (e.g.,
e820), but
>>> only via the device, so exposing this memory via
/sys/firmware/memmap/ is
>>> wrong:
>>>  "kexec needs the raw firmware-provided memory map to setup
the
>>>   parameter segment of the kernel that should be booted with
>>>   kexec. Also, the raw memory map is useful for debugging. For
>>>   that reason, /sys/firmware/memmap is an interface that provides
>>>   the raw memory map to userspace." [1]
>>>
>>> We want to let user space know that memory which is always
detected,
>>> added, and managed via a (device) driver - like memory managed by
>>> virtio-mem - is special. It cannot be used for placing kexec
segments
>>> and the (device) driver is responsible for re-adding memory that
>>> (eventually shrunk/grown/defragmented) memory after a reboot/kexec.
It
>>> should e.g., not be added to a fixed up firmware memmap. However,
it should
>>> be dumped by kdump.
>>>
>>> Also, such memory could behave differently than an ordinary DIMM -
e.g.,
>>> memory managed by virtio-mem can have holes inside added memory
resource,
>>> which should not be touched, especially for writing.
>>>
>>> Let's expose that memory as "System RAM (driver
managed)" e.g., via
>>> /pro/iomem.
>>>
>>> We don't have to worry about firmware_map_remove() on the
removal path.
>>> If there is no entry, it will simply return with -EINVAL.
>>>
>>> [1]
https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-firmware-memmap
>>>
>>> Cc: Andrew Morton <akpm at linux-foundation.org>
>>> Cc: Michal Hocko <mhocko at suse.com>
>>> Cc: Pankaj Gupta <pankaj.gupta.linux at gmail.com>
>>> Cc: Wei Yang <richard.weiyang at gmail.com>
>>> Cc: Baoquan He <bhe at redhat.com>
>>> Cc: Eric Biederman <ebiederm at xmission.com>
>>> Signed-off-by: David Hildenbrand <david at redhat.com>
>>> ---
>>>  include/linux/memory_hotplug.h |  8 ++++++++
>>>  mm/memory_hotplug.c            | 20 ++++++++++++++++----
>>>  2 files changed, 24 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/include/linux/memory_hotplug.h
b/include/linux/memory_hotplug.h
>>> index bf0e3edb8688..cc538584b39e 100644
>>> --- a/include/linux/memory_hotplug.h
>>> +++ b/include/linux/memory_hotplug.h
>>> @@ -68,6 +68,14 @@ struct mhp_params {
>>>       pgprot_t pgprot;
>>>  };
>>>
>>> +/* Flags used for add_memory() and friends. */
>>> +
>>> +/*
>>> + * Don't create entries in /sys/firmware/memmap/ and expose
memory as
>>> + * "System RAM (driver managed)" in e.g., /proc/iomem
>>> + */
>>> +#define MHP_DRIVER_MANAGED           1
>>> +
>>>  /*
>>>   * Zone resizing functions
>>>   *
>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>>> index ebdf6541d074..cfa0721280aa 100644
>>> --- a/mm/memory_hotplug.c
>>> +++ b/mm/memory_hotplug.c
>>> @@ -98,11 +98,11 @@ void mem_hotplug_done(void)
>>>  u64 max_mem_size = U64_MAX;
>>>
>>>  /* add this memory to iomem resource */
>>> -static struct resource *register_memory_resource(u64 start, u64
size)
>>> +static struct resource *register_memory_resource(u64 start, u64
size,
>>> +                                              const char
*resource_name)
>>>  {
>>>       struct resource *res;
>>>       unsigned long flags =  IORESOURCE_SYSTEM_RAM |
IORESOURCE_BUSY;
>>> -     char *resource_name = "System RAM";
>>>
>>>       /*
>>>        * Make sure value parsed from 'mem=' only restricts
memory adding
>>> @@ -1058,7 +1058,8 @@ int __ref add_memory_resource(int nid, struct
resource *res,
>>>       BUG_ON(ret);
>>>
>>>       /* create new memmap entry */
>>> -     firmware_map_add_hotplug(start, start + size, "System
RAM");
>>> +     if (!(flags & MHP_DRIVER_MANAGED))
>>> +             firmware_map_add_hotplug(start, start + size,
"System RAM");
>>>
>>>       /* device_online() will take the lock when calling
online_pages() */
>>>       mem_hotplug_done();
>>> @@ -1081,10 +1082,21 @@ int __ref add_memory_resource(int nid,
struct resource *res,
>>>  /* requires device_hotplug_lock, see add_memory_resource() */
>>>  int __ref __add_memory(int nid, u64 start, u64 size, unsigned long
flags)
>>>  {
>>> +     const char *resource_name = "System RAM";
>>>       struct resource *res;
>>>       int ret;
>>>
>>> -     res = register_memory_resource(start, size);
>>> +     /*
>>> +      * Indicate that memory managed by a driver is special.
It's always
>>> +      * detected and added via a driver, should not be given to
the kexec
>>> +      * kernel for booting when manually crafting the firmware
memmap, and
>>> +      * no kexec segments should be placed on it. However, kdump
should
>>> +      * dump this memory.
>>> +      */
>>> +     if (flags & MHP_DRIVER_MANAGED)
>>> +             resource_name = "System RAM (driver
managed)";
>>> +
>>> +     res = register_memory_resource(start, size, resource_name);
>>>       if (IS_ERR(res))
>>>               return PTR_ERR(res);
>>>
>>>
>>
>> BTW, I was wondering if this is actually also something that
>> drivers/dax/kmem.c wants to use for adding memory.
>>
>> Just because we decided to use some DAX memory in the current kernel as
>> system ram, doesn't mean we should make that decision for the kexec
>> kernel (e.g., using it as initial memory, placing kexec binaries onto
>> it, etc.). This is also not what we would observe during a real reboot.
> 
> Agree.
> 
>> I can see that the "System RAM" resource will show up as
child resource
>> under the device e.g., in /proc/iomem.
>>
>> However, entries in /sys/firmware/memmap/ are created as "System
RAM".
> 
> True. Do you think this rename should just be limited to what type
> /sys/firmware/memmap/ emits? I have the concern, but no proof
We could split this patch into

MHP_NO_FIRMWARE_MEMMAP (create firmware memmap entries)

and

MHP_DRIVER_MANAGED (name of the resource)

See below, the latter might not be needed.
> currently, that there are /proc/iomem walkers that explicitly look for
> "System RAM", but might be thrown off by "System RAM (driver
> managed)". I was not aware of /sys/firmware/memmap until about 5
> minutes ago.
The only two users of /proc/iomem I am aware of are kexec-tools and some
s390x tools.

kexec-tools on x86-64 uses /sys/firmware/memmap to craft the initial
memmap, but uses /proc/iomem to
a) Find places for kexec images
b) Detect memory regions to dump via kdump

I am not yet sure if we really need the "System RAM (driver managed)"
part. If we can teach kexec-tools to
a) Don't place kexec images on "System RAM" that has a parent
resource
(most likely requires kexec-tools changes)
b) Consider for kdump "System RAM" that has a parent resource
we might be able to avoid renaming that. (I assume that's already done)

E.g., regarding virtio-mem (patch #3) I am currently also looking into
creating a parent resource instead, like dax/kmem to avoid the rename:

:/# cat /proc/iomem
00000000-00000fff : Reserved
[...]
100000000-13fffffff : System RAM
140000000-33fffffff : virtio0
  140000000-147ffffff : System RAM
  148000000-14fffffff : System RAM
  150000000-157ffffff : System RAM
340000000-303fffffff : virtio1
  340000000-347ffffff : System RAM
3280000000-32ffffffff : PCI Bus 0000:00



-- 
Thanks,

David / dhildenb

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