On Tue, 2022-03-08 at 23:37 +0000, Sean Christopherson wrote: > 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. Question: is it worth it? Since I am very busy with various things, this feature, beeing just small debug help which I used once in a while doesn't get much time from me. I can implement this in the future no doubt. Best regards, Maxim Levitsky > > The param should also be "unsafe". I didn't knew about unsafe parameters until recently. I can mark it as such, no objections. Best regards, Maxim Levitsky > > 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); >
