x86/mm: Add .bss..decrypted section to hold shared variables

kvmclock defines few static variables which are shared with the
hypervisor during the kvmclock initialization.

When SEV is active, memory is encrypted with a guest-specific key, and
if the guest OS wants to share the memory region with the hypervisor
then it must clear the C-bit before sharing it.

Currently, we use kernel_physical_mapping_init() to split large pages
before clearing the C-bit on shared pages. But it fails when called from
the kvmclock initialization (mainly because the memblock allocator is
not ready that early during boot).

Add a __bss_decrypted section attribute which can be used when defining
such shared variable. The so-defined variables will be placed in the
.bss..decrypted section. This section will be mapped with C=0 early
during boot.

The .bss..decrypted section has a big chunk of memory that may be unused
when memory encryption is not active, free it when memory encryption is
not active.

Suggested-by: Thomas Gleixner <[email protected]>
Signed-off-by: Brijesh Singh <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: Tom Lendacky <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Sean Christopherson <[email protected]>
Cc: Radim Krčmář<[email protected]>
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]

0 files changed, 0 insertions, 0 deletions