When building a kernel with CONFIG_PARAVIRT_XXL the paravirt
infrastructure will always use functions for reading or writing MSRs,
even when running on bare metal.
Switch to inline RDMSR/WRMSR instructions in this case, reducing the
paravirt overhead.
The first patch is a prerequisite fix for alternative patching. Its
is needed due to the initial indirect call needs to be padded with
NOPs in some cases with the following patches.
In order to make this less intrusive, some further reorganization of
the MSR access helpers is done in the patches 1-6.
The next 4 patches are converting the non-paravirt case to use direct
inlining of the MSR access instructions, including the WRMSRNS
instruction and the immediate variants of RDMSR and WRMSR if possible.
Patches 11-13 are some further preparations for making the real switch
to directly patch in the native MSR instructions easier.
Patch 14 is switching the paravirt MSR function interface from normal
call ABI to one more similar to the native MSR instructions.
Patch 15 is a little cleanup patch.
Patch 16 is the final step for patching in the native MSR instructions
when not running as a Xen PV guest.
This series has been tested to work with Xen PV and on bare metal.
Note that there is more room for improvement. This series is sent out
to get a first impression how the code will basically look like.
Right now the same problem is solved differently for the paravirt and
the non-paravirt cases. In case this is not desired, there are two
possibilities to merge the two implementations. Both solutions have
the common idea to have rather similar code for paravirt and
non-paravirt variants, but just use a different main macro for
generating the respective code. For making the code of both possible
scenarios more similar, the following variants are possible:
1. Remove the micro-optimizations of the non-paravirt case, making
it similar to the paravirt code in my series. This has the
advantage of being more simple, but might have a very small
negative performance impact (probably not really detectable).
2. Add the same micro-optimizations to the paravirt case, requiring
to enhance paravirt patching to support a to be patched indirect
call in the middle of the initial code snipplet.
In both cases the native MSR function variants would no longer be
usable in the paravirt case, but this would mostly affect Xen, as it
would need to open code the WRMSR/RDMSR instructions to be used
instead the native_*msr*() functions.
Changes since V2:
- switch back to the paravirt approach
Changes since V1:
- Use Xin Li's approach for inlining
- Several new patches
Juergen Gross (16):
x86/alternative: Support alt_replace_call() with instructions after
call
coco/tdx: Rename MSR access helpers
x86/sev: Replace call of native_wrmsr() with native_wrmsrq()
KVM: x86: Remove the KVM private read_msr() function
x86/msr: Minimize usage of native_*() msr access functions
x86/msr: Move MSR trace calls one function level up
x86/opcode: Add immediate form MSR instructions
x86/extable: Add support for immediate form MSR instructions
x86/msr: Use the alternatives mechanism for WRMSR
x86/msr: Use the alternatives mechanism for RDMSR
x86/alternatives: Add ALTERNATIVE_4()
x86/paravirt: Split off MSR related hooks into new header
x86/paravirt: Prepare support of MSR instruction interfaces
x86/paravirt: Switch MSR access pv_ops functions to instruction
interfaces
x86/msr: Reduce number of low level MSR access helpers
x86/paravirt: Use alternatives for MSR access with paravirt
arch/x86/coco/sev/internal.h | 7 +-
arch/x86/coco/tdx/tdx.c | 8 +-
arch/x86/hyperv/ivm.c | 2 +-
arch/x86/include/asm/alternative.h | 6 +
arch/x86/include/asm/fred.h | 2 +-
arch/x86/include/asm/kvm_host.h | 10 -
arch/x86/include/asm/msr.h | 345 ++++++++++++++++------
arch/x86/include/asm/paravirt-msr.h | 148 ++++++++++
arch/x86/include/asm/paravirt.h | 67 -----
arch/x86/include/asm/paravirt_types.h | 57 ++--
arch/x86/include/asm/qspinlock_paravirt.h | 4 +-
arch/x86/kernel/alternative.c | 5 +-
arch/x86/kernel/cpu/mshyperv.c | 7 +-
arch/x86/kernel/kvmclock.c | 2 +-
arch/x86/kernel/paravirt.c | 42 ++-
arch/x86/kvm/svm/svm.c | 16 +-
arch/x86/kvm/vmx/tdx.c | 2 +-
arch/x86/kvm/vmx/vmx.c | 8 +-
arch/x86/lib/x86-opcode-map.txt | 5 +-
arch/x86/mm/extable.c | 35 ++-
arch/x86/xen/enlighten_pv.c | 52 +++-
arch/x86/xen/pmu.c | 4 +-
tools/arch/x86/lib/x86-opcode-map.txt | 5 +-
tools/objtool/check.c | 1 +
24 files changed, 576 insertions(+), 264 deletions(-)
create mode 100644 arch/x86/include/asm/paravirt-msr.h
--
2.53.0
