linux-kernel - [PATCH v7 0/5] x86: Fix SEV guest regression

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Date:   Mon, 10 Sep 2018 16:49:06 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...e.de>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: [PATCH v7 0/5] x86: Fix SEV guest regression

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@....com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Borislav Petkov <bp@...e.de>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Sean Christopherson <sean.j.christopherson@...el.com>
Cc: "Radim Krčmář" <rkrcmar@...hat.com>

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 (5):
  x86/mm: Restructure sme_encrypt_kernel()
  x86/mm: Enhance 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(-)

-- 
2.7.4