Re: [RFC PATCH 15/31] efi_memory: add an event handler to update memory map

[Heinrich Schuchardt]

Am 12. Juni 2024 04:42:00 MESZ schrieb Simon Glass <sjg at chromium.org>:
>Hi Tom,
>
>On Tue, 11 Jun 2024 at 16:54, Tom Rini <trini at konsulko.com> wrote:
>>
>> On Tue, Jun 11, 2024 at 04:22:25PM -0600, Simon Glass wrote:
>> > Hi Tom,
>> >
>> > On Tue, 11 Jun 2024 at 15:01, Tom Rini <trini at konsulko.com> wrote:
>> > >
>> > > On Tue, Jun 11, 2024 at 12:52:19PM -0600, Simon Glass wrote:
>> > > > Hi,
>> > > >
>> > > > On Tue, 11 Jun 2024 at 08:36, Tom Rini <trini at konsulko.com> wrote:
>> > > > >
>> > > > > On Tue, Jun 11, 2024 at 12:17:16PM +0200, Heinrich Schuchardt wrote:
>> > > > > > On 07.06.24 20:52, Sughosh Ganu wrote:
>> > > > > > > There are events that would be used to notify other interested modules
>> > > > > > > of any changes in available and occupied memory. This would happen
>> > > > > > > when a module allocates or reserves memory, or frees up memory. These
>> > > > > > > changes in memory map should be notified to other interested modules
>> > > > > > > so that the allocated memory does not get overwritten. Add an event
>> > > > > > > handler in the EFI memory module to update the EFI memory map
>> > > > > > > accordingly when such changes happen. As a consequence, any subsequent
>> > > > > > > memory request would honour the updated memory map and only available
>> > > > > > > memory would be allocated from.
>> > > > > > >
>> > > > > > > Signed-off-by: Sughosh Ganu <sughosh.ganu at linaro.org>
>> > > > > > > ---
>> > > > > > >   lib/efi_loader/efi_memory.c | 70 ++++++++++++++++++++++++++++++-------
>> > > > > > >   1 file changed, 58 insertions(+), 12 deletions(-)
>> > > > > > >
>> > > > > > > diff --git a/lib/efi_loader/efi_memory.c b/lib/efi_loader/efi_memory.c
>> > > > > > > index 435e580fb3..93244161b0 100644
>> > > > > > > --- a/lib/efi_loader/efi_memory.c
>> > > > > > > +++ b/lib/efi_loader/efi_memory.c
>> > > > > > > @@ -73,6 +73,10 @@ struct efi_pool_allocation {
>> > > > > > >   #if CONFIG_IS_ENABLED(MEM_MAP_UPDATE_NOTIFY)
>> > > > > > >   extern bool is_addr_in_ram(uintptr_t addr);
>> > > > > > >
>> > > > > > > +static efi_status_t __efi_add_memory_map_pg(u64 start, u64 pages,
>> > > > > > > +                                       int memory_type,
>> > > > > > > +                                       bool overlap_only_ram);
>> > > > > > > +
>> > > > > > >   static void efi_map_update_notify(u64 addr, u64 size, u8 op)
>> > > > > > >   {
>> > > > > > >     struct event_efi_mem_map_update efi_map = {0};
>> > > > > > > @@ -84,6 +88,34 @@ static void efi_map_update_notify(u64 addr, u64 size, u8 op)
>> > > > > > >     if (is_addr_in_ram((uintptr_t)addr))
>> > > > > > >             event_notify(EVT_EFI_MEM_MAP_UPDATE, &efi_map, sizeof(efi_map));
>> > > > > > >   }
>> > > > > > > +
>> > > > > > > +static int lmb_mem_map_update_sync(void *ctx, struct event *event)
>> > > > > > > +{
>> > > > > > > +   u8 op;
>> > > > > > > +   u64 addr;
>> > > > > > > +   u64 pages;
>> > > > > > > +   efi_status_t status;
>> > > > > > > +   struct event_lmb_map_update *lmb_map = &event->data.lmb_map;
>> > > > > > > +
>> > > > > > > +   addr = (uintptr_t)map_sysmem(lmb_map->base, 0);
>> > > > > > > +   pages = efi_size_in_pages(lmb_map->size + (addr & EFI_PAGE_MASK));
>> > > > > > > +   op = lmb_map->op;
>> > > > > > > +   addr &= ~EFI_PAGE_MASK;
>> > > > > > > +
>> > > > > > > +   if (op != MAP_OP_RESERVE && op != MAP_OP_FREE) {
>> > > > > > > +           log_debug("Invalid map update op received (%d)\n", op);
>> > > > > > > +           return -1;
>> > > > > > > +   }
>> > > > > > > +
>> > > > > > > +   status = __efi_add_memory_map_pg(addr, pages,
>> > > > > > > +                                    op == MAP_OP_FREE ?
>> > > > > > > +                                    EFI_CONVENTIONAL_MEMORY :
>> > > > > >
>> > > > > > This is dangerous. LMB might turn memory that is marked as
>> > > > > > EfiReservedMemory which the OS must respect into EfiBootServicesData
>> > > > > > which the OS may discard.
>> > > > > >
>> > > > > > E.g. initr_lmb() is being called after efi_memory_init().
>> > > > > >
>> > > > > > Getting all cases of synchronization properly tested seems very hard to
>> > > > > > me. Everything would be much easier if we had only a single memory
>> > > > > > management system.
>> > > > >
>> > > > > Yes, Sughosh is working on the single memory reservation system for
>> > > > > everyone to use. This pairs with the single memory allocation system
>> > > > > (malloc) that we have. Parts of the code base that aren't keeping these
>> > > > > systems up to date / obeying their results need to be corrected.
>> > > >
>> > > > The EFI allocations don't happen until boot time...so why do we need
>> > > > to do this now? We can instead have an EFI function to scan LMB and
>> > > > add to its memory map.
>> > >
>> > > We're talking about reservations, not allocations. So yes, when someone
>> > > is making their reservation, they need to make it. I don't understand
>> > > your question.
>> >
>> > As I understand it, this is used to tell EFI about a memory reservation.
>>
>> This patch, or this series? This series isn't about EFI. This patch is,
>> yes.
>>
>> > But the EFI code can scan the LMB reservations just before booting and
>> > update its tables. I don't see a need to keep them in sync before the
>> > boot actually happens.
>>
>> But that wouldn't work. If something needs to reserve a region it needs
>> to do it when it starts using it. It's not about the EFI map for the OS,
>> it's about making sure that U-Boot doesn't scribble over a now-reserved
>> area.
>
>I'm not convinced of that yet. EFI does not do allocations until it
>starts loading images, and it uses LMB for those (or at least it does
>with bootstd). I'm just trying to keep this all as simple as possible.

You can load a boot time EFI driver which keeps running while you return to U-Boot to load another file.

The background activity of the EFI driver binary can result in any number of allocations.

Best regards

Heinrich


>
>Regards,
>Simon