On Sun, Oct 07, 2018 at 19:09:01 -0700, Richard Henderson wrote: > On 10/6/18 2:45 PM, Emilio G. Cota wrote: > > Currently we evict an entry to the victim TLB when it doesn't match > > the current address. But it could be that there's no match because > > the current entry is invalid. Do not evict the entry to the vtlb > > in that case. > > > > This change will help us keep track of the TLB's use rate. > > > > Signed-off-by: Emilio G. Cota <c...@braap.org> > > --- > > include/exec/cpu-all.h | 14 ++++++++++++++ > > accel/tcg/cputlb.c | 2 +- > > 2 files changed, 15 insertions(+), 1 deletion(-) > > > > diff --git a/include/exec/cpu-all.h b/include/exec/cpu-all.h > > index 117d2fbbca..d938dedafc 100644 > > --- a/include/exec/cpu-all.h > > +++ b/include/exec/cpu-all.h > > @@ -362,6 +362,20 @@ static inline bool tlb_hit(target_ulong tlb_addr, > > target_ulong addr) > > return tlb_hit_page(tlb_addr, addr & TARGET_PAGE_MASK); > > } > > > > +/** > > + * tlb_is_valid - return true if at least one of the addresses is valid > > + * @te: pointer to CPUTLBEntry > > + * > > + * This is useful when we don't have a particular address to compare > > against, > > + * and we just want to know whether any entry holds valid data. > > + */ > > +static inline bool tlb_is_valid(const CPUTLBEntry *te) > > +{ > > + return !(te->addr_read & TLB_INVALID_MASK) || > > + !(te->addr_write & TLB_INVALID_MASK) || > > + !(te->addr_code & TLB_INVALID_MASK); > > +} > > No, I think you misunderstand. > > First, TLB_INVALID_MASK is only ever set for addr_write, in response to > PAGE_WRITE_INV. Second, an entry that is invalid for write is still valid for > read+exec. So there is benefit to swapping it out to the victim cache. > > This is used by the s390x target to make the "lowpage" read-only, which is a > special architected 512 byte range within pages 0 and 1. This is done by > forcing writes, but not reads, back through tlb_fill.
Aah I see. The point is to avoid pushing to the victim cache an entry that is all invalid, not just partially invalid. Thanks for the clarification! Emilio