On Tue, Feb 08, 2022, Maxim Levitsky wrote: > On Thu, 2021-09-02 at 16:56 +0000, Sean Christopherson wrote: > > Assuming this hasn't been abandoned... > > > > On Wed, Aug 11, 2021, Maxim Levitsky wrote: > > > This parameter will be used by VMX and SVM code to force > > > interception of a set of exceptions, given by a bitmask > > > for guest debug and/or kvm debug. > > > > > > This is based on an idea first shown here: > > > https://patchwork.kernel.org/project/kvm/patch/20160301192822.GD22677@xxxxxxx/ > > > > > > CC: Borislav Petkov <bp@xxxxxxx> > > > Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx> > > > --- > > > arch/x86/kvm/x86.c | 3 +++ > > > arch/x86/kvm/x86.h | 2 ++ > > > 2 files changed, 5 insertions(+) > > > > > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > > > index fdc0c18339fb..092e2fad3c0d 100644 > > > --- a/arch/x86/kvm/x86.c > > > +++ b/arch/x86/kvm/x86.c > > > @@ -184,6 +184,9 @@ module_param(force_emulation_prefix, bool, S_IRUGO); > > > int __read_mostly pi_inject_timer = -1; > > > module_param(pi_inject_timer, bint, S_IRUGO | S_IWUSR); > > > > > > +uint force_intercept_exceptions_mask; > > > +module_param(force_intercept_exceptions_mask, uint, S_IRUGO | S_IWUSR); > > > > Use octal permissions. This also can't be a simple writable param, at least not > > without a well-documented disclaimer, as there's no guarantee a vCPU will update > > its exception bitmap in a timely fashion. An alternative to a module param would > > be to extend/add a per-VM ioctl(), e.g. maybe KVM_SET_GUEST_DEBUG? The downside > > of an ioctl() is that it would require userspace enabling :-/ > > > > All other module params in this file use macros for permissions, that is why > I used them too. > > I'll add a comment with a disclaimer here - this is only for debug. > I strongly don't want to have this as ioctl as that will indeed need qemu patches, > not to mention things like unit tests and which don't even always use qemu. > > Or I can make this parameter read-only. I don't mind reloading kvm module when > I change this parameter. Oh! We can force an update, a la nx_huge_pages, where the setter loops through all VMs and does a kvm_make_all_cpus_request() to instruct vCPUs to update their bitmaps. Requires a new request, but that doesn't seem like a huge deal, and it might help pave the way for adding more debug hooks for developers. The param should also be "unsafe". E.g. something like static const struct kernel_param_ops force_ex_intercepts_ops = { .set = set_force_exception_intercepts, .get = get_force_exception_intercepts, }; module_param_cb_unsafe(force_exception_intercepts, &force_ex_intercepts_ops, &force_exception_intercepts, 0644);
