[PATCH v6 0/5] x86: Fix SEV guest regression

From: Brijesh Singh
Date: Fri Sep 07 2018 - 13:57:46 EST


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@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Cc: "Radim KrÄmÃÅ" <rkrcmar@xxxxxxxxxx>

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 (5):
x86/mm: Restructure sme_encrypt_kernel()
x86/mm: fix sme_populate_pgd() to update page flags
x86/mm: add .data..decrypted section to hold shared variables
x86/kvm: use __decrypted attribute in shared variables
x86/kvm: Avoid dynamic allocation of pvclock data when SEV is active

arch/x86/include/asm/mem_encrypt.h | 10 ++
arch/x86/kernel/head64.c | 11 ++
arch/x86/kernel/kvmclock.c | 18 ++-
arch/x86/kernel/vmlinux.lds.S | 20 ++++
arch/x86/mm/init.c | 3 +
arch/x86/mm/mem_encrypt.c | 10 ++
arch/x86/mm/mem_encrypt_identity.c | 232 +++++++++++++++++++++++++++----------
7 files changed, 240 insertions(+), 64 deletions(-)

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2.7.4