[v1,2/3] mm/memory_hotplug: Introduce MHP_DRIVER_MANAGED
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Message ID 20200429160803.109056-3-david@redhat.com
State New
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  • mm/memory_hotplug: Make virtio-mem play nicely with kexec-tools
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Commit Message

David Hildenbrand April 29, 2020, 4:08 p.m. UTC
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@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 include/linux/memory_hotplug.h |  8 ++++++++
 mm/memory_hotplug.c            | 20 ++++++++++++++++----
 2 files changed, 24 insertions(+), 4 deletions(-)

Comments

David Hildenbrand April 30, 2020, 7:19 a.m. UTC | #1
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@linux-foundation.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
> Cc: Wei Yang <richard.weiyang@gmail.com>
> Cc: Baoquan He <bhe@redhat.com>
> Cc: Eric Biederman <ebiederm@xmission.com>
> Signed-off-by: David Hildenbrand <david@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".
Dan Williams April 30, 2020, 8:11 a.m. UTC | #2
On Thu, Apr 30, 2020 at 12:20 AM David Hildenbrand <david@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@linux-foundation.org>
> > Cc: Michal Hocko <mhocko@suse.com>
> > Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
> > Cc: Wei Yang <richard.weiyang@gmail.com>
> > Cc: Baoquan He <bhe@redhat.com>
> > Cc: Eric Biederman <ebiederm@xmission.com>
> > Signed-off-by: David Hildenbrand <david@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 April 30, 2020, 8:20 a.m. UTC | #3
On 30.04.20 10:11, Dan Williams wrote:
> On Thu, Apr 30, 2020 at 12:20 AM David Hildenbrand <david@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@linux-foundation.org>
>>> Cc: Michal Hocko <mhocko@suse.com>
>>> Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
>>> Cc: Wei Yang <richard.weiyang@gmail.com>
>>> Cc: Baoquan He <bhe@redhat.com>
>>> Cc: Eric Biederman <ebiederm@xmission.com>
>>> Signed-off-by: David Hildenbrand <david@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
Dan Williams April 30, 2020, 8:34 a.m. UTC | #4
On Thu, Apr 30, 2020 at 1:21 AM David Hildenbrand <david@redhat.com> wrote:
> >> 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

Looks good to me if it flies with kexec-tools.

Patch
diff mbox series

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);