On Fri, Jan 12, 2018 at 12:03:10AM +0100, Thomas Gleixner wrote:
On Thu, 11 Jan 2018, Thomas Gleixner wrote:
On Thu, 11 Jan 2018, Thomas Gleixner wrote:
On Thu, 11 Jan 2018, Linus Torvalds wrote:
On Thu, Jan 11, 2018 at 12:37 PM, Thomas Gleixner tglx@linutronix.de wrote:
67a9108ed431 ("x86/efi: Build our own page table structures")
got rid of EFI depending on real_mode_header->trampoline_pgd
So I think it only got rid of by default - the codepath is still there, the allocation is still there, it's just that it's not actually used unless somebody does that "efi=old_mmap" thing.
Yes, the trampoline_pgd is still around, but I can't figure out how it would be used after boot. Confused, digging more.
So coming back to the same commit. From the changelog:
This is caused by mapping EFI regions with RWX permissions. There isn't much we can do to restrict the permissions for these regions due to the way the firmware toolchains mix code and data, but we can at least isolate these mappings so that they do not appear in the regular kernel page tables.In commit d2f7cbe7b26a ("x86/efi: Runtime services virtual mapping") we started using 'trampoline_pgd' to map the EFI regions because there was an existing identity mapping there which we use during the SetVirtualAddressMap() call and for broken firmware that accesses those addresses.
So this very commit gets rid of the (ab)use of trampoline_pgd and allocates efi_pgd, which we made use the proper size.
trampoline_pgd is since then only used to get into long mode in realmode/rm/trampoline_64.S and for reboot in machine_real_restart().
The runtime services stuff does not use it in kernel versions >= 4.6
But there is one very well hidden user for it after boot:
It's used for booting secondary CPUs from real modeSo the transition to long mode for secondaries uses the trampoline pgd for long mode transition and then jumping to secondary_startup_64 where CR3 is set to the real kernel page tables.
Ok, so the summary is that this patch is only needed for the 4.4 and 4.9 kernels, and _NOT_ for Linus's tree and 4.14, right?
thanks,
greg k-h