Re: [PATCH 03/12] KVM: arm64: Report hardware dirty status of stage2 PTE if coverred
Hi Steven, On 2020/7/1 19:28, Steven Price wrote: > 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 >> --- >> 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. > OK. >> + */ >> +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(_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. > oh yes. Here we can use a local copy to get higher performance. I am not sure here has problem about correctness. I *think* we should always acquire corresponding lock before manipulate PTs, so there is no other agent will update PTs during our several PTs access (except MMU, but it just modifies AF and [S2]AP) . But do I miss something? >> +do { >> +old_pteval = pteval; >> +pteval = cmpxchg_relaxed(_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? > Aha, I have changed the code for several times and it is equal to xchg_relaxed now, thanks. I use _relaxd here because I am not clear about the reason that we use _relaxed in kvm_set_s2XXX_XXX and use dsb() in kvm_set_pte. But I will correct this in patch v2. >> + >> +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. > After my test, you are right ;-) . Thanks, Keqian > Steve > >> static inline void kvm_set_pmd(pmd_t *pmdp, pmd_t new_pmd) >> { >> > > . > ___ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
Re: [PATCH 03/12] KVM: arm64: Report hardware dirty status of stage2 PTE if coverred
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 --- 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(_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(_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) { ___ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
[PATCH 03/12] KVM: arm64: Report hardware dirty status of stage2 PTE if coverred
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 --- 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. + */ +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(_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)); + do { + old_pteval = pteval; + pteval = cmpxchg_relaxed(_val(*ptep), old_pteval, new_pteval); + } while (pteval != old_pteval); + + 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 */ static inline void kvm_set_pmd(pmd_t *pmdp, pmd_t new_pmd) { -- 2.19.1 ___ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm