Messages in this thread Patch in this message | | | Date | Tue, 1 Nov 2022 10:32:04 -0700 | From | Josh Poimboeuf <> | Subject | Re: [PATCH 1/7] KVM: VMX: remove regs argument of __vmx_vcpu_run |
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On Mon, Oct 31, 2022 at 05:37:46PM +0000, Sean Christopherson wrote: > On Fri, Oct 28, 2022, Paolo Bonzini wrote: > > Registers are reachable through vcpu_vmx, no need to pass > > a separate pointer to the regs[] array. > > > > No functional change intended. > > > > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> > > --- > > arch/x86/kernel/asm-offsets.c | 1 + > > arch/x86/kvm/vmx/nested.c | 3 +- > > arch/x86/kvm/vmx/vmenter.S | 58 +++++++++++++++-------------------- > > arch/x86/kvm/vmx/vmx.c | 3 +- > > arch/x86/kvm/vmx/vmx.h | 3 +- > > 5 files changed, 29 insertions(+), 39 deletions(-) > > > > diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c > > index cb50589a7102..90da275ad223 100644 > > --- a/arch/x86/kernel/asm-offsets.c > > +++ b/arch/x86/kernel/asm-offsets.c > > @@ -111,6 +111,7 @@ static void __used common(void) > > > > if (IS_ENABLED(CONFIG_KVM_INTEL)) { > > BLANK(); > > + OFFSET(VMX_vcpu_arch_regs, vcpu_vmx, vcpu.arch.regs); > > Is there an asm-offsets-like solution that doesn't require exposing vcpu_vmx > outside of KVM? We (Google) want to explore loading multiple instances of KVM, > i.e. loading multiple versions of kvm.ko at the same time, to allow intra-host > migration between versions of KVM to upgrade/rollback KVM without changing the > kernel (RFC coming soon-ish). IIRC, asm-offsets is the only place where I haven't > been able to figure out a simple way to avoid exposing KVM's internal structures > outside of KVM (so that the structures can change across KVM instances without > breaking kernel code).
Is that really a problem? Would it even make sense for non-KVM kernel code to use 'vcpu_vmx' anyway? It already seems to be private. asm-offsets.c has to "cheat" to get access to it by including "../kvm/vmx/vmx.h".
So the only concern is exposing the asm offsets, right? But it seems highly unlikely any non-KVM code would be using those either.
And, that would be a bug anyway: module code is subject to change and could always get recompiled. The kernel proper shouldn't be making any assumptions about the layouts of module-owned structs.
-- Josh
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