Messages in this thread | | | From | "Singh, Balbir" <> | Subject | Re: [PATCH v3 3/5] arch/x86/mm: Refactor cond_ibpb() to support other use cases | Date | Tue, 21 Apr 2020 03:46:59 +0000 |
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On Sat, 2020-04-18 at 11:59 +0200, Thomas Gleixner wrote: > > "Singh, Balbir" <sblbir@amazon.com> writes: > > On Fri, 2020-04-17 at 15:07 +0200, Thomas Gleixner wrote: > > > > > > Balbir Singh <sblbir@amazon.com> writes: > > > > > > > > /* > > > > - * Use bit 0 to mangle the TIF_SPEC_IB state into the mm pointer > > > > which is > > > > - * stored in cpu_tlb_state.last_user_mm_ibpb. > > > > + * Bits to mangle the TIF_SPEC_IB state into the mm pointer which is > > > > + * stored in cpu_tlb_state.last_user_mm_spec. > > > > */ > > > > #define LAST_USER_MM_IBPB 0x1UL > > > > +#define LAST_USER_MM_SPEC_MASK (LAST_USER_MM_IBPB) > > > > > > > > /* Reinitialize tlbstate. */ > > > > - this_cpu_write(cpu_tlbstate.last_user_mm_ibpb, > > > > LAST_USER_MM_IBPB); > > > > + this_cpu_write(cpu_tlbstate.last_user_mm_spec, > > > > LAST_USER_MM_IBPB); > > > > > > Shouldn't that be LAST_USER_MM_MASK? > > > > > > > No, that crashes the system for SW flushes, because it tries to flush the > > L1D > > via the software loop and early enough we don't have the l1d_flush_pages > > allocated. LAST_USER_MM_MASK has LAST_USER_MM_FLUSH_L1D bit set. > > You can trivially prevent this by checking l1d_flush_pages != NULL. >
But why would we want to flush on reinit? It is either coming back from a low power state or initialising, is it worth adding a check for != NULL everytime we flush to handle this case?
Thanks, Balbir
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