| Message ID | 20210326031654.3716-3-wangyanan55@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: arm64: Improve efficiency of stage2 page table | expand |
Hi Yanan, On 3/26/21 3:16 AM, Yanan Wang wrote: > With a guest translation fault, the memcache pages are not needed if KVM > is only about to install a new leaf entry into the existing page table. > And with a guest permission fault, the memcache pages are also not needed > for a write_fault in dirty-logging time if KVM is only about to update > the existing leaf entry instead of collapsing a block entry into a table. > > By comparing fault_granule and vma_pagesize, cases that require allocations > from memcache and cases that don't can be distinguished completely. > > Signed-off-by: Yanan Wang <wangyanan55@huawei.com> > --- > arch/arm64/kvm/mmu.c | 25 ++++++++++++------------- > 1 file changed, 12 insertions(+), 13 deletions(-) > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index 1eec9f63bc6f..05af40dc60c1 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -810,19 +810,6 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > gfn = fault_ipa >> PAGE_SHIFT; > mmap_read_unlock(current->mm); > > - /* > - * Permission faults just need to update the existing leaf entry, > - * and so normally don't require allocations from the memcache. The > - * only exception to this is when dirty logging is enabled at runtime > - * and a write fault needs to collapse a block entry into a table. > - */ > - if (fault_status != FSC_PERM || (logging_active && write_fault)) { > - ret = kvm_mmu_topup_memory_cache(memcache, > - kvm_mmu_cache_min_pages(kvm)); > - if (ret) > - return ret; > - } > - > mmu_seq = vcpu->kvm->mmu_notifier_seq; > /* > * Ensure the read of mmu_notifier_seq happens before we call > @@ -880,6 +867,18 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > else if (cpus_have_const_cap(ARM64_HAS_CACHE_DIC)) > prot |= KVM_PGTABLE_PROT_X; > > + /* > + * Allocations from the memcache are required only when granule of the > + * lookup level where the guest fault happened exceeds vma_pagesize, > + * which means new page tables will be created in the fault handlers. > + */ > + if (fault_granule > vma_pagesize) { > + ret = kvm_mmu_topup_memory_cache(memcache, > + kvm_mmu_cache_min_pages(kvm)); > + if (ret) > + return ret; > + } As I explained in v1 [1], this looks correct to me. I still think that someone else should have a look, but if Marc decides to pick up this patch as-is, he can add my Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>. [1] https://lore.kernel.org/lkml/2c65bff2-be7f-b20c-9265-939bc73185b6@arm.com/ Thanks, Alex > + > /* > * Under the premise of getting a FSC_PERM fault, we just need to relax > * permissions only if vma_pagesize equals fault_granule. Otherwise,
On 2021/4/7 23:35, Alexandru Elisei wrote: > Hi Yanan, > > On 3/26/21 3:16 AM, Yanan Wang wrote: >> With a guest translation fault, the memcache pages are not needed if KVM >> is only about to install a new leaf entry into the existing page table. >> And with a guest permission fault, the memcache pages are also not needed >> for a write_fault in dirty-logging time if KVM is only about to update >> the existing leaf entry instead of collapsing a block entry into a table. >> >> By comparing fault_granule and vma_pagesize, cases that require allocations >> from memcache and cases that don't can be distinguished completely. >> >> Signed-off-by: Yanan Wang <wangyanan55@huawei.com> >> --- >> arch/arm64/kvm/mmu.c | 25 ++++++++++++------------- >> 1 file changed, 12 insertions(+), 13 deletions(-) >> >> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c >> index 1eec9f63bc6f..05af40dc60c1 100644 >> --- a/arch/arm64/kvm/mmu.c >> +++ b/arch/arm64/kvm/mmu.c >> @@ -810,19 +810,6 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, >> gfn = fault_ipa >> PAGE_SHIFT; >> mmap_read_unlock(current->mm); >> >> - /* >> - * Permission faults just need to update the existing leaf entry, >> - * and so normally don't require allocations from the memcache. The >> - * only exception to this is when dirty logging is enabled at runtime >> - * and a write fault needs to collapse a block entry into a table. >> - */ >> - if (fault_status != FSC_PERM || (logging_active && write_fault)) { >> - ret = kvm_mmu_topup_memory_cache(memcache, >> - kvm_mmu_cache_min_pages(kvm)); >> - if (ret) >> - return ret; >> - } >> - >> mmu_seq = vcpu->kvm->mmu_notifier_seq; >> /* >> * Ensure the read of mmu_notifier_seq happens before we call >> @@ -880,6 +867,18 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, >> else if (cpus_have_const_cap(ARM64_HAS_CACHE_DIC)) >> prot |= KVM_PGTABLE_PROT_X; >> >> + /* >> + * Allocations from the memcache are required only when granule of the >> + * lookup level where the guest fault happened exceeds vma_pagesize, >> + * which means new page tables will be created in the fault handlers. >> + */ >> + if (fault_granule > vma_pagesize) { >> + ret = kvm_mmu_topup_memory_cache(memcache, >> + kvm_mmu_cache_min_pages(kvm)); >> + if (ret) >> + return ret; >> + } > As I explained in v1 [1], this looks correct to me. I still think that someone > else should have a look, but if Marc decides to pick up this patch as-is, he can > add my Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>. Thanks again for this, Alex! Hi Marc, Will, Any thoughts about this patch? Thanks, Yanan > [1] https://lore.kernel.org/lkml/2c65bff2-be7f-b20c-9265-939bc73185b6@arm.com/ > > Thanks, > > Alex > >> + >> /* >> * Under the premise of getting a FSC_PERM fault, we just need to relax >> * permissions only if vma_pagesize equals fault_granule. Otherwise, > .
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index 1eec9f63bc6f..05af40dc60c1 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c @@ -810,19 +810,6 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, gfn = fault_ipa >> PAGE_SHIFT; mmap_read_unlock(current->mm); - /* - * Permission faults just need to update the existing leaf entry, - * and so normally don't require allocations from the memcache. The - * only exception to this is when dirty logging is enabled at runtime - * and a write fault needs to collapse a block entry into a table. - */ - if (fault_status != FSC_PERM || (logging_active && write_fault)) { - ret = kvm_mmu_topup_memory_cache(memcache, - kvm_mmu_cache_min_pages(kvm)); - if (ret) - return ret; - } - mmu_seq = vcpu->kvm->mmu_notifier_seq; /* * Ensure the read of mmu_notifier_seq happens before we call @@ -880,6 +867,18 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, else if (cpus_have_const_cap(ARM64_HAS_CACHE_DIC)) prot |= KVM_PGTABLE_PROT_X; + /* + * Allocations from the memcache are required only when granule of the + * lookup level where the guest fault happened exceeds vma_pagesize, + * which means new page tables will be created in the fault handlers. + */ + if (fault_granule > vma_pagesize) { + ret = kvm_mmu_topup_memory_cache(memcache, + kvm_mmu_cache_min_pages(kvm)); + if (ret) + return ret; + } + /* * Under the premise of getting a FSC_PERM fault, we just need to relax * permissions only if vma_pagesize equals fault_granule. Otherwise,
With a guest translation fault, the memcache pages are not needed if KVM is only about to install a new leaf entry into the existing page table. And with a guest permission fault, the memcache pages are also not needed for a write_fault in dirty-logging time if KVM is only about to update the existing leaf entry instead of collapsing a block entry into a table. By comparing fault_granule and vma_pagesize, cases that require allocations from memcache and cases that don't can be distinguished completely. Signed-off-by: Yanan Wang <wangyanan55@huawei.com> --- arch/arm64/kvm/mmu.c | 25 ++++++++++++------------- 1 file changed, 12 insertions(+), 13 deletions(-)