On 28 September 2016 at 16:54, Arnd Bergmann <arnd@xxxxxxxx> wrote: > On Thursday 22 September 2016, Ard Biesheuvel wrote: >> ================================================================================ >> NOTE: this is a work in progress, and not fully functional yet. In particular, >> the actual MMC host protocol methods are stubbed out at the moment, and need to >> be wired up to the Linux device drivers. >> ================================================================================ >> >> On mobile and embedded systems, there is usually only a single MMC device for >> non-volatile storage, which sits behind a controller that is owned by the OS at >> runtime. This makes it difficult to host the UEFI variable store on MMC as well, >> since the UEFI runtime services routines expect ownership of the underlying >> device as well. >> >> This series proposes an approach to work around this. It implements the UEFI >> MMC host protocol in the kernel, in a way that makes it possible to expose it >> to the firmware. At the same time, the firmware needs be set up for this, i.e., >> it needs to expose its MMC host protocol pointer via a UEFI configuration table, >> so that the kernel can override it if it decides to expose this functionality >> to the firmware. >> >> Note that these patches are based on patches in the EFI tree that are queued >> for v4.9, which replace the runtime wrappers spinlock with a semaphore. This >> allows us to sleep in the firmware callbacks. > > Would it be possible to implement the UEFI varstore more generally on top > of the Linux pstore interface and then have a pstore backend on top of > MMC? That could give us very similar behavior, but also a bit more flexibility. > It would be a bit confusing to have the 'dmesg' pstore target on top of > UEFI varstore which in turn is on top of pstore on MMC, but I think that's > ok as long as we prevent recursion. > The reason for choosing MMC over block I/O or other more generic interfaces is that it should also allow firmware implementations that support UEFI secure boot using RPMB/MMC, where the authentication and the RPMB related crypto are performed by a secure world component that talks to the firmware directly. -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
