| Message ID | 20200218232953.5724-1-sean.j.christopherson@intel.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | KVM: x86: Allow userspace to disable the emulator | expand |
On 19/02/20 00:29, Sean Christopherson wrote: > The primary intent of this series is to dynamically allocate the emulator > and get KVM to a state where the emulator *could* be disabled at some > point in the future. Actually allowing userspace to disable the emulator > was a minor change at that point, so I threw it in. > > Dynamically allocating the emulator shrinks the size of x86 vcpus by > ~2.5k bytes, which is important because 'struct vcpu_vmx' has once again > fattened up and squeaked past the PAGE_ALLOC_COSTLY_ORDER threshold. > Moving the emulator to its own allocation gives us some breathing room > for the near future, and has some other nice side effects. > > As for disabling the emulator... in the not-too-distant future, I expect > there will be use cases that can truly disable KVM's emulator, e.g. for > security (KVM's and/or the guests). I don't have a strong opinion on > whether or not KVM should actually allow userspace to disable the emulator > without a concrete use case (unless there already is a use case?), which > is why that part is done in its own tiny patch. > > Running without an emulator has been "tested" in the sense that the > selftests that don't require emulation continue to pass, and everything > else fails with the expected "emulation error". I agree with Vitaly that, if we want this, it should be a KVM_ENABLE_CAP instead. The first 10 patches are very nice cleanups though so I plan to apply them (with Vitaly's suggested nits for review) after you answer the question on patch 10. Paolo > > v2: > - Rebase to kvm/queue, 2c2787938512 ("KVM: selftests: Stop ...") > > Sean Christopherson (13): > KVM: x86: Refactor I/O emulation helpers to provide vcpu-only variant > KVM: x86: Explicitly pass an exception struct to check_intercept > KVM: x86: Move emulation-only helpers to emulate.c > KVM: x86: Refactor R/W page helper to take the emulation context > KVM: x86: Refactor emulated exception injection to take the emul > context > KVM: x86: Refactor emulate tracepoint to explicitly take context > KVM: x86: Refactor init_emulate_ctxt() to explicitly take context > KVM: x86: Dynamically allocate per-vCPU emulation context > KVM: x86: Move kvm_emulate.h into KVM's private directory > KVM: x86: Shrink the usercopy region of the emulation context > KVM: x86: Add helper to "handle" internal emulation error > KVM: x86: Add variable to control existence of emulator > KVM: x86: Allow userspace to disable the kernel's emulator > > arch/x86/include/asm/kvm_host.h | 12 +- > arch/x86/kvm/emulate.c | 13 +- > arch/x86/{include/asm => kvm}/kvm_emulate.h | 9 +- > arch/x86/kvm/mmu/mmu.c | 1 + > arch/x86/kvm/svm.c | 5 +- > arch/x86/kvm/trace.h | 22 +-- > arch/x86/kvm/vmx/vmx.c | 15 +- > arch/x86/kvm/x86.c | 193 +++++++++++++------- > arch/x86/kvm/x86.h | 12 +- > 9 files changed, 183 insertions(+), 99 deletions(-) > rename arch/x86/{include/asm => kvm}/kvm_emulate.h (99%) >
On Mon, Mar 02, 2020 at 07:42:31PM +0100, Paolo Bonzini wrote: > On 19/02/20 00:29, Sean Christopherson wrote: > > The primary intent of this series is to dynamically allocate the emulator > > and get KVM to a state where the emulator *could* be disabled at some > > point in the future. Actually allowing userspace to disable the emulator > > was a minor change at that point, so I threw it in. > > > > Dynamically allocating the emulator shrinks the size of x86 vcpus by > > ~2.5k bytes, which is important because 'struct vcpu_vmx' has once again > > fattened up and squeaked past the PAGE_ALLOC_COSTLY_ORDER threshold. > > Moving the emulator to its own allocation gives us some breathing room > > for the near future, and has some other nice side effects. > > > > As for disabling the emulator... in the not-too-distant future, I expect > > there will be use cases that can truly disable KVM's emulator, e.g. for > > security (KVM's and/or the guests). I don't have a strong opinion on > > whether or not KVM should actually allow userspace to disable the emulator > > without a concrete use case (unless there already is a use case?), which > > is why that part is done in its own tiny patch. > > > > Running without an emulator has been "tested" in the sense that the > > selftests that don't require emulation continue to pass, and everything > > else fails with the expected "emulation error". > > I agree with Vitaly that, if we want this, it should be a KVM_ENABLE_CAP > instead. The first 10 patches are very nice cleanups though so I plan > to apply them (with Vitaly's suggested nits for review) after you answer > the question on patch 10. Works for me, thanks!
The primary intent of this series is to dynamically allocate the emulator and get KVM to a state where the emulator *could* be disabled at some point in the future. Actually allowing userspace to disable the emulator was a minor change at that point, so I threw it in. Dynamically allocating the emulator shrinks the size of x86 vcpus by ~2.5k bytes, which is important because 'struct vcpu_vmx' has once again fattened up and squeaked past the PAGE_ALLOC_COSTLY_ORDER threshold. Moving the emulator to its own allocation gives us some breathing room for the near future, and has some other nice side effects. As for disabling the emulator... in the not-too-distant future, I expect there will be use cases that can truly disable KVM's emulator, e.g. for security (KVM's and/or the guests). I don't have a strong opinion on whether or not KVM should actually allow userspace to disable the emulator without a concrete use case (unless there already is a use case?), which is why that part is done in its own tiny patch. Running without an emulator has been "tested" in the sense that the selftests that don't require emulation continue to pass, and everything else fails with the expected "emulation error". v2: - Rebase to kvm/queue, 2c2787938512 ("KVM: selftests: Stop ...") Sean Christopherson (13): KVM: x86: Refactor I/O emulation helpers to provide vcpu-only variant KVM: x86: Explicitly pass an exception struct to check_intercept KVM: x86: Move emulation-only helpers to emulate.c KVM: x86: Refactor R/W page helper to take the emulation context KVM: x86: Refactor emulated exception injection to take the emul context KVM: x86: Refactor emulate tracepoint to explicitly take context KVM: x86: Refactor init_emulate_ctxt() to explicitly take context KVM: x86: Dynamically allocate per-vCPU emulation context KVM: x86: Move kvm_emulate.h into KVM's private directory KVM: x86: Shrink the usercopy region of the emulation context KVM: x86: Add helper to "handle" internal emulation error KVM: x86: Add variable to control existence of emulator KVM: x86: Allow userspace to disable the kernel's emulator arch/x86/include/asm/kvm_host.h | 12 +- arch/x86/kvm/emulate.c | 13 +- arch/x86/{include/asm => kvm}/kvm_emulate.h | 9 +- arch/x86/kvm/mmu/mmu.c | 1 + arch/x86/kvm/svm.c | 5 +- arch/x86/kvm/trace.h | 22 +-- arch/x86/kvm/vmx/vmx.c | 15 +- arch/x86/kvm/x86.c | 193 +++++++++++++------- arch/x86/kvm/x86.h | 12 +- 9 files changed, 183 insertions(+), 99 deletions(-) rename arch/x86/{include/asm => kvm}/kvm_emulate.h (99%)