Messages in this thread | | | Date | Fri, 4 Feb 2022 12:06:31 -0800 | From | Ira Weiny <> | Subject | Re: [PATCH V8 08/44] x86/fault: Adjust WARN_ON for PKey fault |
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On Fri, Jan 28, 2022 at 03:10:24PM -0800, Dave Hansen wrote: > On 1/27/22 09:54, ira.weiny@intel.com wrote: > > From: Ira Weiny <ira.weiny@intel.com> > > > > Previously if a Protection key fault occurred it indicated something > > very wrong because user page mappings are not supposed to be in the > > kernel address space. > > This is missing a key point. The problem is PK faults on "*kernel* > addresses.
Ok, I'll try and clarify.
> > > Now PKey faults may happen on kernel mappings if the feature is enabled. > > One nit: I've been using "pkeys" and "pkey" as the terms. I usually > don't capitalize them except at the beginning of a sentence.
I'll audit the series to use lower case for consistency.
> > > If PKS is enabled, avoid the warning in the fault path. > > > > Cc: Sean Christopherson <seanjc@google.com> > > Cc: Dan Williams <dan.j.williams@intel.com> > > Signed-off-by: Ira Weiny <ira.weiny@intel.com> > > --- > > arch/x86/mm/fault.c | 12 ++++++++---- > > 1 file changed, 8 insertions(+), 4 deletions(-) > > > > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c > > index d0074c6ed31a..6ed91b632eac 100644 > > --- a/arch/x86/mm/fault.c > > +++ b/arch/x86/mm/fault.c > > @@ -1148,11 +1148,15 @@ do_kern_addr_fault(struct pt_regs *regs, unsigned long hw_error_code, > > unsigned long address) > > { > > /* > > - * Protection keys exceptions only happen on user pages. We > > - * have no user pages in the kernel portion of the address > > - * space, so do not expect them here. > > + * X86_PF_PK (Protection key exceptions) may occur on kernel addresses > > + * when PKS (PKeys Supervisor) is enabled. > > + * > > + * However, if PKS is not enabled WARN if this exception is seen > > + * because there are no user pages in the kernel portion of the address > > + * space. > > */ > > - WARN_ON_ONCE(hw_error_code & X86_PF_PK); > > + WARN_ON_ONCE(!cpu_feature_enabled(X86_FEATURE_PKS) && > > + (hw_error_code & X86_PF_PK)); > > > > #ifdef CONFIG_X86_32 > > /* > > I'm wondering if this warning is even doing us any good. I'm pretty > sure it's never triggered on me at least. Either way, let's not get too > carried away with the comment. I think this should do: > > /* > * PF_PF faults should only occur on kernel > * addresses when supervisor pkeys are enabled. > */
Sounds better, Ira
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