Messages in this thread | | | Subject | Re: [PATCH 03/12] KVM: arm64: Report hardware dirty status of stage2 PTE if coverred | From | Steven Price <> | Date | Wed, 1 Jul 2020 12:28:08 +0100 |
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Hi,
On 16/06/2020 10:35, Keqian Zhu wrote: > kvm_set_pte is called to replace a target PTE with a desired one. > We always do this without changing the desired one, but if dirty > status set by hardware is coverred, let caller know it. > > Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com> > --- > arch/arm64/kvm/mmu.c | 36 +++++++++++++++++++++++++++++++++++- > 1 file changed, 35 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index 5ad87bce23c0..27407153121b 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -194,11 +194,45 @@ static void clear_stage2_pmd_entry(struct kvm *kvm, pmd_t *pmd, phys_addr_t addr > put_page(virt_to_page(pmd)); > } > > -static inline void kvm_set_pte(pte_t *ptep, pte_t new_pte) > +#ifdef CONFIG_ARM64_HW_AFDBM > +/** > + * @ret: true if dirty status set by hardware is coverred.
NIT: s/coverred/covered/, this is in several places.
> + */ > +static bool kvm_set_pte(pte_t *ptep, pte_t new_pte) > +{ > + pteval_t old_pteval, new_pteval, pteval; > + bool old_logging, new_no_write; > + > + old_logging = kvm_hw_dbm_enabled() && !pte_none(*ptep) && > + kvm_s2pte_dbm(ptep); > + new_no_write = pte_none(new_pte) || kvm_s2pte_readonly(&new_pte); > + > + if (!old_logging || !new_no_write) { > + WRITE_ONCE(*ptep, new_pte); > + dsb(ishst); > + return false; > + } > + > + new_pteval = pte_val(new_pte); > + pteval = READ_ONCE(pte_val(*ptep));
This usage of *ptep looks wrong - it's read twice using READ_ONCE (once in kvm_s2pte_dbm()) and once without any decoration (in the pte_none() call). Which looks a bit dodgy and at the very least needs some justification. AFAICT you would be better taking a local copy and using that rather than reading from memory repeatedly.
> + do { > + old_pteval = pteval; > + pteval = cmpxchg_relaxed(&pte_val(*ptep), old_pteval, new_pteval); > + } while (pteval != old_pteval); This look appears to be reinventing xchg_relaxed(). Any reason we can't just use xchg_relaxed()? Also we had a dsb() after the WRITE_ONCE but you are using the _relaxed variant here. What is the justification for not having a barrier?
> + > + return !kvm_s2pte_readonly(&__pte(pteval)); > +} > +#else > +/** > + * @ret: true if dirty status set by hardware is coverred. > + */ > +static inline bool kvm_set_pte(pte_t *ptep, pte_t new_pte) > { > WRITE_ONCE(*ptep, new_pte); > dsb(ishst); > + return false; > } > +#endif /* CONFIG_ARM64_HW_AFDBM */
You might be able to avoid this #ifdef by redefining old_logging as:
old_logging = IS_ENABLED(CONFIG_ARM64_HW_AFDBM) && ...
I *think* the compiler should be able to kill the dead code and leave you with just the above when the config symbol is off.
Steve
> > static inline void kvm_set_pmd(pmd_t *pmdp, pmd_t new_pmd) > { >
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