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@pd.tni...
CC: Borislav Petkov bp@suse.de Signed-off-by: Maxim Levitsky mlevitsk@redhat.com
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);