[PATCH v8 0/2] x86: Fix SEV guest regression

Brijesh Singh
2018-09-13T21:51:27Z

The following commit

"
x86/kvmclock: Remove memblock dependency

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=368a540e0232ad446931f5a4e8a5e06f69f21343
"

introduced SEV guest regression.

The guest physical address holding the wall_clock and hv_clock_boot
are shared with the hypervisor must be mapped with C=0 when SEV
is active. To clear the C-bit we use kernel_physical_mapping_init() to
split the large pages. The above commit moved the kvmclock initialization
very early and kernel_physical_mapping_init() fails to allocate memory
while spliting the large page.

To solve it, we add a special .data..decrypted section, this section can be
used to hold the shared variables. Early boot code maps this section with
C=0. The section is pmd aligned and sized to avoid the need to split the pages.
Caller can use __decrypted attribute to add the variables in .data..decrypted
section.

Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>

NOTE: Since there was some design changes based on Thomas G suggestion hence I
dropped Acked and R-b from Tom, Paolo and Boris.

Changes since v7:
- As per Thomas Gleixner suggestion move the decrypted data in .bss..decrypted section
- remove the second auxiliary array from SEV case
- allocate memory for pvclock data pointer early and map with C=0 for SEV case

Changes since v6:
- improve commit messages
- rename free_decrypted_mem -> mem_encrypt_free_decrypted_mem

Changes since v5:
- rename hvclock_boot_dec -> hvclock_boot_aux.
- rename section from .data..decrypted_aux -> .data..decrypted.aux.
- use NR_CPUS instead of random number elements in hv_clock_aux variable.

Changes since v4:
- define few static pages in .data..decrypted which can be used
for cpus > HVC_BOOT_ARRAY_SIZE when SEV is active.

Changes since v3:
- commit message improvements (based on Sean's feedback)

Changes since v2:
- commit message and code comment improvements (based on Boris feedback)
- move sme_populate_pgd fixes in new patch.
- drop stable Cc - will submit to stable after patch is upstreamed.

Changes since v1:
- move the logic to re-arrange mapping in new patch
- move the definition of __start_data_* in mem_encrypt.h
- map the workarea buffer as encrypted when SEV is enabled
- enhance the sme_populate_pgd to update the pte/pmd flags when mapping exist

Brijesh Singh (2):
x86/mm: add .bss..decrypted section to hold shared variables
x86/kvm: use __bss_decrypted attribute in shared variables

arch/x86/include/asm/mem_encrypt.h | 7 +++++++
arch/x86/kernel/head64.c | 16 +++++++++++++++
arch/x86/kernel/kvmclock.c | 42 +++++++++++++++++++++++++++++++++++---
arch/x86/kernel/vmlinux.lds.S | 19 +++++++++++++++++
arch/x86/mm/init.c | 4 ++++
arch/x86/mm/mem_encrypt.c | 10 +++++++++
6 files changed, 95 insertions(+), 3 deletions(-)

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2.7.4