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. r~