History log of /linux-master/arch/x86/kernel/cpu/feat_ctl.c
Revision Date Author Comments
# 332bfc7b 19-Mar-2021 Sean Christopherson <seanjc@google.com>

x86/cpu/intel: Allow SGX virtualization without Launch Control support

The kernel will currently disable all SGX support if the hardware does
not support launch control. Make it more permissive to allow SGX
virtualization on systems without Launch Control support. This will
allow KVM to expose SGX to guests that have less-strict requirements on
the availability of flexible launch control.

Improve error message to distinguish between three cases. There are two
cases where SGX support is completely disabled:
1) SGX has been disabled completely by the BIOS
2) SGX LC is locked by the BIOS. Bare-metal support is disabled because
of LC unavailability. SGX virtualization is unavailable (because of
One where it is partially available:
3) SGX LC is locked by the BIOS. Bare-metal support is disabled because
of LC unavailability. SGX virtualization is supported.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Co-developed-by: Kai Huang <kai.huang@intel.com>
Signed-off-by: Kai Huang <kai.huang@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
Acked-by: Dave Hansen <dave.hansen@intel.com>
Link: https://lkml.kernel.org/r/b3329777076509b3b601550da288c8f3c406a865.1616136308.git.kai.huang@intel.com

# e9a15a40 19-Mar-2021 Kai Huang <kai.huang@intel.com>

x86/cpufeatures: Make SGX_LC feature bit depend on SGX bit

Move SGX_LC feature bit to CPUID dependency table to make clearing all
SGX feature bits easier. Also remove clear_sgx_caps() since it is just
a wrapper of setup_clear_cpu_cap(X86_FEATURE_SGX) now.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Kai Huang <kai.huang@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Acked-by: Dave Hansen <dave.hansen@intel.com>
Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
Link: https://lkml.kernel.org/r/5d4220fd0a39f52af024d3fa166231c1d498dd10.1616136308.git.kai.huang@intel.com

# 38853a30 12-Nov-2020 Jarkko Sakkinen <jarkko@kernel.org>

x86/cpu/intel: Add a nosgx kernel parameter

Add a kernel parameter to disable SGX kernel support and document it.

[ bp: Massage. ]

Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Acked-by: Jethro Beekman <jethro@fortanix.com>
Tested-by: Sean Christopherson <sean.j.christopherson@intel.com>
Link: https://lkml.kernel.org/r/20201112220135.165028-9-jarkko@kernel.org

# 224ab352 12-Nov-2020 Sean Christopherson <seanjc@google.com>

x86/cpu/intel: Detect SGX support

Kernel support for SGX is ultimately decided by the state of the launch
control bits in the feature control MSR (MSR_IA32_FEAT_CTL). If the
hardware supports SGX, but neglects to support flexible launch control, the
kernel will not enable SGX.

Enable SGX at feature control MSR initialization and update the associated
X86_FEATURE flags accordingly. Disable X86_FEATURE_SGX (and all
derivatives) if the kernel is not able to establish itself as the authority
over SGX Launch Control.

All checks are performed for each logical CPU (not just boot CPU) in order
to verify that MSR_IA32_FEATURE_CONTROL is correctly configured on all
CPUs. All SGX code in this series expects the same configuration from all

This differs from VMX where X86_FEATURE_VMX is intentionally cleared only
for the current CPU so that KVM can provide additional information if KVM
fails to load like which CPU doesn't support VMX. There’s not much the
kernel or an administrator can do to fix the situation, so SGX neglects to
convey additional details about these kinds of failures if they occur.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Co-developed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Jethro Beekman <jethro@fortanix.com>
Link: https://lkml.kernel.org/r/20201112220135.165028-8-jarkko@kernel.org

# 0e79ad86 23-Mar-2020 Benjamin Thiel <b.thiel@posteo.de>

x86/cpu: Fix a -Wmissing-prototypes warning for init_ia32_feat_ctl()

Add a missing include in order to fix -Wmissing-prototypes warning:

arch/x86/kernel/cpu/feat_ctl.c:95:6: warning: no previous prototype for ‘init_ia32_feat_ctl’ [-Wmissing-prototypes]
95 | void init_ia32_feat_ctl(struct cpuinfo_x86 *c)

Signed-off-by: Benjamin Thiel <b.thiel@posteo.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200323105934.26597-1-b.thiel@posteo.de

# bb02e2cb 14-Jan-2020 Sean Christopherson <seanjc@google.com>

x86/cpu: Print "VMX disabled" error message iff KVM is enabled

Don't print an error message about VMX being disabled by BIOS if KVM,
the sole user of VMX, is disabled. E.g. if KVM is disabled and the MSR
is unlocked, the kernel will intentionally disable VMX when locking
feature control and then complain that "BIOS" disabled VMX.

Fixes: ef4d3bf19855 ("x86/cpu: Clear VMX feature flag if VMX is not fully enabled")
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200114202545.20296-1-sean.j.christopherson@intel.com

# 85c17291 20-Dec-2019 Sean Christopherson <seanjc@google.com>

x86/cpufeatures: Add flag to track whether MSR IA32_FEAT_CTL is configured

Add a new feature flag, X86_FEATURE_MSR_IA32_FEAT_CTL, to track whether
IA32_FEAT_CTL has been initialized. This will allow KVM, and any future
subsystems that depend on IA32_FEAT_CTL, to rely purely on cpufeatures
to query platform support, e.g. allows a future patch to remove KVM's
manual IA32_FEAT_CTL MSR checks.

Various features (on platforms that support IA32_FEAT_CTL) are dependent
on IA32_FEAT_CTL being configured and locked, e.g. VMX and LMCE. The
MSR is always configured during boot, but only if the CPU vendor is
recognized by the kernel. Because CPUID doesn't incorporate the current
IA32_FEAT_CTL value in its reporting of relevant features, it's possible
for a feature to be reported as supported in cpufeatures but not truly
enabled, e.g. if the CPU supports VMX but the kernel doesn't recognize
the CPU.

As a result, without the flag, KVM would see VMX as supported even if
IA32_FEAT_CTL hasn't been initialized, and so would need to manually
read the MSR and check the various enabling bits to avoid taking an
unexpected #GP on VMXON.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20191221044513.21680-14-sean.j.christopherson@intel.com

# 167a4894 20-Dec-2019 Sean Christopherson <seanjc@google.com>

x86/cpu: Set synthetic VMX cpufeatures during init_ia32_feat_ctl()

Set the synthetic VMX cpufeatures, which need to be kept to preserve
/proc/cpuinfo's ABI, in the common IA32_FEAT_CTL initialization code.
Remove the vendor code that manually sets the synthetic flags.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20191221044513.21680-13-sean.j.christopherson@intel.com

# b47ce1fe 20-Dec-2019 Sean Christopherson <seanjc@google.com>

x86/cpu: Detect VMX features on Intel, Centaur and Zhaoxin CPUs

Add an entry in struct cpuinfo_x86 to track VMX capabilities and fill
the capabilities during IA32_FEAT_CTL MSR initialization.

Make the VMX capabilities dependent on IA32_FEAT_CTL and
X86_FEATURE_NAMES so as to avoid unnecessary overhead on CPUs that can't
possibly support VMX, or when /proc/cpuinfo is not available.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20191221044513.21680-11-sean.j.christopherson@intel.com

# ef4d3bf1 20-Dec-2019 Sean Christopherson <seanjc@google.com>

x86/cpu: Clear VMX feature flag if VMX is not fully enabled

Now that IA32_FEAT_CTL is always configured and locked for CPUs that are
known to support VMX[*], clear the VMX capability flag if the MSR is
unsupported or BIOS disabled VMX, i.e. locked IA32_FEAT_CTL and didn't
set the appropriate VMX enable bit.

[*] Because init_ia32_feat_ctl() is called from vendors ->c_init(), it's
still possible for IA32_FEAT_CTL to be left unlocked when VMX is
supported by the CPU. This is not fatal, and will be addressed in a
future patch.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20191221044513.21680-9-sean.j.christopherson@intel.com

# 1db2a6e1 20-Dec-2019 Sean Christopherson <seanjc@google.com>

x86/intel: Initialize IA32_FEAT_CTL MSR at boot

Opportunistically initialize IA32_FEAT_CTL to enable VMX when the MSR is
left unlocked by BIOS. Configuring feature control at boot time paves
the way for similar enabling of other features, e.g. Software Guard
Extensions (SGX).

Temporarily leave equivalent KVM code in place in order to avoid
introducing a regression on Centaur and Zhaoxin CPUs, e.g. removing
KVM's code would leave the MSR unlocked on those CPUs and would break
existing functionality if people are loading kvm_intel on Centaur and/or
Zhaoxin. Defer enablement of the boot-time configuration on Centaur and
Zhaoxin to future patches to aid bisection.

Note, Local Machine Check Exceptions (LMCE) are also supported by the
kernel and enabled via feature control, but the kernel currently uses
LMCE if and only if the feature is explicitly enabled by BIOS. Keep
the current behavior to avoid introducing bugs, future patches can opt
in to opportunistic enabling if it's deemed desirable to do so.

Always lock IA32_FEAT_CTL if it exists, even if the CPU doesn't support
VMX, so that other existing and future kernel code that queries the MSR
can assume it's locked.

Start from a clean slate when constructing the value to write to
IA32_FEAT_CTL, i.e. ignore whatever value BIOS left in the MSR so as not
to enable random features or fault on the WRMSR.

Suggested-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20191221044513.21680-5-sean.j.christopherson@intel.com