[PATCH 3/4] efi_loader: preserve installer images in pmem

[Ilias Apalodimas]

On Mon, 11 Nov 2024 at 10:05, Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
>
> On 10/25/24 13:14, Sughosh Ganu wrote:
> > From: Ilias Apalodimas <ilias.apalodimas at linaro.org>
> >
> > One of the problems OS installers face, when running in EFI, is that
> > the mounted ISO after calling ExitBootServices goes away. For some
> > distros this is a problem since they rely on finding some core packages
> > before continuing the installation. Distros have works around this --
> > e.g Fedora has a special kernel command line parameter called
> > inst.stage2 [0].
> >
> > ACPI has NFIT and NVDIMM support to provide ramdisks to the OS, but we
> > don't have anything in place for DTs. Linux and device trees have support
> > for persistent memory devices.
> >
> > It's worth noting that for linux to instantiate the /dev/pmemX device,
> > the memory described in the pmem node has to be omitted from the EFI
> > memory map we hand over to the OS if ZONE_DEVICES and SPARSEMEM is
> > enabled. With those enabled the pmem driver ends up calling
> > devm_memremap_pages() instead of devm_memremap(). The latter works
> > whether the memory is omitted or marked as reserved, but mapping pages
> > only works if the memory is omitted.
> >
> > On top of that, depending on how the kernel is configured, that memory
> > area must be page aligned or 2MB aligned. PowerPC is an exception here
> > and requires 16MB alignment, but since we don't have EFI support for
> > it, limit the alignment to 2MB.
> >
> > Ensure that the ISO image is 2MB aligned and remove the region
> > occupied by the image from the EFI memory map.
> >
> > Signed-off-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
> > Signed-off-by: Sughosh Ganu <sughosh.ganu at linaro.org>
> > ---
> >   lib/efi_loader/efi_bootmgr.c | 22 +++++++++++++++++-----
> >   1 file changed, 17 insertions(+), 5 deletions(-)
> >
> > diff --git a/lib/efi_loader/efi_bootmgr.c b/lib/efi_loader/efi_bootmgr.c
> > index a3aa2b8d1b..16f75555f6 100644
> > --- a/lib/efi_loader/efi_bootmgr.c
> > +++ b/lib/efi_loader/efi_bootmgr.c
> > @@ -18,6 +18,8 @@
> >   #include <efi_loader.h>
> >   #include <efi_variable.h>
> >   #include <asm/unaligned.h>
> > +#include <linux/kernel.h>
> > +#include <linux/sizes.h>
> >
> >   static const struct efi_boot_services *bs;
> >   static const struct efi_runtime_services *rs;
> > @@ -358,13 +360,16 @@ static efi_status_t prepare_loaded_image(u16 *label, ulong addr, ulong size,
> >       }
> >
> >       /*
> > -      * TODO: expose the ramdisk to OS.
> > -      * Need to pass the ramdisk information by the architecture-specific
> > -      * methods such as 'pmem' device-tree node.
> > +      * Linux supports 'pmem' which allows OS installers to find, reclaim
> > +      * the mounted images and continue the installation since the contents
> > +      * of the pmem region are treated as local media.
> > +      *
> > +      * The memory regions used for it needs to be carved out of the EFI
> > +      * memory map.
> >        */
> > -     ret = efi_add_memory_map(addr, size, EFI_RESERVED_MEMORY_TYPE);
> > +     ret = efi_remove_memory_map(addr, size, EFI_CONVENTIONAL_MEMORY);
> >       if (ret != EFI_SUCCESS) {
> > -             log_err("Memory reservation failed\n");
> > +             log_err("Failed to reserve memory\n");
> >               goto err;
> >       }
> >
> > @@ -486,6 +491,13 @@ static efi_status_t try_load_from_uri_path(struct efi_device_path_uri *uridp,
> >               ret = EFI_INVALID_PARAMETER;
> >               goto err;
> >       }
> > +     /*
> > +      * Depending on the kernel configuration, pmem memory area must be page
> > +      * aligned or 2MB aligned. PowerPC is an exception here and requires
> > +      * 16MB alignment, but since we don't have EFI support for it, limit
> > +      * the alignment to 2MB.
> > +      */
> > +     image_size = ALIGN(image_size, SZ_2M);
>
> The code regarding .iso and .img handling seems to be misplaced. Why
> should we treat a file loaded from a block device differently to a file
> loaded from the network?

If the installer is located in a block device, the kernel will find
the image when it scans those devices during boot. It's only when we
have it on a memory area that we need to preserve it

Thanks
/Ilias
>
> Best regards
>
> Heinrich
>
> >
> >       /*
> >        * If the file extension is ".iso" or ".img", mount it and try to load
>