| Message ID | 20210811122927.900604-3-mlevitsk@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: my debug patch queue | expand |
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.tnic/ > > 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 :-/
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.tnic/ > > > > 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. Best regards, Maxim Levitsky PS: Forgot to send this mail, it was in my drafts folder.
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.tnic/ > > > > > > 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. 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);
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.tnic/ > > > > > > > > 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); >
On 3/9/22 13:31, Maxim Levitsky wrote: > 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 agree it's not very much worth. Paolo
On Wed, Mar 09, 2022, Paolo Bonzini wrote: > On 3/9/22 13:31, Maxim Levitsky wrote: > > 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 agree it's not very much worth. I don't have a use case, was just trying to find the bottom of my inbox and came across this thread.
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); +EXPORT_SYMBOL_GPL(force_intercept_exceptions_mask); /* * Restoring the host value for MSRs that are only consumed when running in * usermode, e.g. SYSCALL MSRs and TSC_AUX, can be deferred until the CPU diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h index 7d66d63dc55a..2b59825213c7 100644 --- a/arch/x86/kvm/x86.h +++ b/arch/x86/kvm/x86.h @@ -347,6 +347,8 @@ extern struct static_key kvm_no_apic_vcpu; extern bool report_ignored_msrs; +extern uint force_intercept_exceptions_mask; + static inline u64 nsec_to_cycles(struct kvm_vcpu *vcpu, u64 nsec) { return pvclock_scale_delta(nsec, vcpu->arch.virtual_tsc_mult,
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.tnic/ 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(+)