Re: [PATCH 1/2] KVM: async_pf: kill the unnecessary use_mm/unuse_mm async_pf_execute()
Il 28/04/2014 16:06, Andrea Arcangeli ha scritto: > > "task" is only used to increment task_struct->xxx_flt. I don't think > async_pf_execute() actually needs this (current is PF_WQ_WORKER after > all), but I didn't dare to do another change in the code I can hardly > understand. Considering the faults would be randomly distributed among the kworker threads my preference would also be for NULL instead of current. ptrace and uprobes tends to be the only two places that look into other mm with gup, ptrace knows the exact pid that it is triggering the fault into, so it also can specify the correct task so the fault goes in the right task struct. uprobes uses NULL. KVM knows the correct task (it was in current when kvm_create_vm was called), and doing accounting right would be nice. But I agree that NULL is less misleading than a dummy current, and I applied patch 3 too. Paolo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 1/2] KVM: async_pf: kill the unnecessary use_mm/unuse_mm async_pf_execute()
Hi, On Wed, Apr 23, 2014 at 09:32:28PM +0200, Oleg Nesterov wrote: > On 04/22, Christian Borntraeger wrote: > > > > On 22/04/14 22:15, Christian Borntraeger wrote: > > > On 21/04/14 15:25, Oleg Nesterov wrote: > > >> async_pf_execute() has no reasons to adopt apf->mm, gup(current, mm) > > >> should work just fine even if current has another or NULL ->mm. > > >> > > >> Recently kvm_async_page_present_sync() was added insedie the "use_mm" > > >> section, but it seems that it doesn't need current->mm too. > > >> > > >> Signed-off-by: Oleg Nesterov > > > > > > Indeed, use/unuse_mm should only be necessary for copy_to/from_user etc. > > > This is fine for s390, but it seems that x86 > > > kvm_arch_async_page_not_present > > > might call apf_put_user which might call copy_to_user, so this is not ok, > > > I guess. > > > > wanted to say kvm_arch_async_page_not_present, but I have to correct myself. > > x86 does the "page is there" in the cpu loop, not in the worker. The cpu > > look > > d oes have a valid mm. So this patch should be also ok. > > Thanks ;) > > Btw, I forgot to mention this in the changelog, but > > > >> @@ -80,12 +80,10 @@ static void async_pf_execute(struct work_struct > > >> *work) > > >> > > >> might_sleep(); > > >> > > >> -use_mm(mm); > > >> down_read(>mmap_sem); > > >> get_user_pages(current, mm, addr, 1, 1, 0, NULL, NULL); > > >> up_read(>mmap_sem); > > >> kvm_async_page_present_sync(vcpu, apf); > > >> -unuse_mm(mm); > > it can actually do > > get_user_pages(NULL, mm, addr, 1, 1, 0, NULL, NULL); > > "task" is only used to increment task_struct->xxx_flt. I don't think > async_pf_execute() actually needs this (current is PF_WQ_WORKER after > all), but I didn't dare to do another change in the code I can hardly > understand. Considering the faults would be randomly distributed among the kworker threads my preference would also be for NULL instead of current. ptrace and uprobes tends to be the only two places that look into other mm with gup, ptrace knows the exact pid that it is triggering the fault into, so it also can specify the correct task so the fault goes in the right task struct. uprobes uses NULL. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 1/2] KVM: async_pf: kill the unnecessary use_mm/unuse_mm async_pf_execute()
Hi, On Wed, Apr 23, 2014 at 09:32:28PM +0200, Oleg Nesterov wrote: On 04/22, Christian Borntraeger wrote: On 22/04/14 22:15, Christian Borntraeger wrote: On 21/04/14 15:25, Oleg Nesterov wrote: async_pf_execute() has no reasons to adopt apf-mm, gup(current, mm) should work just fine even if current has another or NULL -mm. Recently kvm_async_page_present_sync() was added insedie the use_mm section, but it seems that it doesn't need current-mm too. Signed-off-by: Oleg Nesterov o...@redhat.com Indeed, use/unuse_mm should only be necessary for copy_to/from_user etc. This is fine for s390, but it seems that x86 kvm_arch_async_page_not_present might call apf_put_user which might call copy_to_user, so this is not ok, I guess. wanted to say kvm_arch_async_page_not_present, but I have to correct myself. x86 does the page is there in the cpu loop, not in the worker. The cpu look d oes have a valid mm. So this patch should be also ok. Thanks ;) Btw, I forgot to mention this in the changelog, but @@ -80,12 +80,10 @@ static void async_pf_execute(struct work_struct *work) might_sleep(); -use_mm(mm); down_read(mm-mmap_sem); get_user_pages(current, mm, addr, 1, 1, 0, NULL, NULL); up_read(mm-mmap_sem); kvm_async_page_present_sync(vcpu, apf); -unuse_mm(mm); it can actually do get_user_pages(NULL, mm, addr, 1, 1, 0, NULL, NULL); task is only used to increment task_struct-xxx_flt. I don't think async_pf_execute() actually needs this (current is PF_WQ_WORKER after all), but I didn't dare to do another change in the code I can hardly understand. Considering the faults would be randomly distributed among the kworker threads my preference would also be for NULL instead of current. ptrace and uprobes tends to be the only two places that look into other mm with gup, ptrace knows the exact pid that it is triggering the fault into, so it also can specify the correct task so the fault goes in the right task struct. uprobes uses NULL. -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 1/2] KVM: async_pf: kill the unnecessary use_mm/unuse_mm async_pf_execute()
Il 28/04/2014 16:06, Andrea Arcangeli ha scritto: task is only used to increment task_struct-xxx_flt. I don't think async_pf_execute() actually needs this (current is PF_WQ_WORKER after all), but I didn't dare to do another change in the code I can hardly understand. Considering the faults would be randomly distributed among the kworker threads my preference would also be for NULL instead of current. ptrace and uprobes tends to be the only two places that look into other mm with gup, ptrace knows the exact pid that it is triggering the fault into, so it also can specify the correct task so the fault goes in the right task struct. uprobes uses NULL. KVM knows the correct task (it was in current when kvm_create_vm was called), and doing accounting right would be nice. But I agree that NULL is less misleading than a dummy current, and I applied patch 3 too. Paolo -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 1/2] KVM: async_pf: kill the unnecessary use_mm/unuse_mm async_pf_execute()
On 04/22, Christian Borntraeger wrote: > > On 22/04/14 22:15, Christian Borntraeger wrote: > > On 21/04/14 15:25, Oleg Nesterov wrote: > >> async_pf_execute() has no reasons to adopt apf->mm, gup(current, mm) > >> should work just fine even if current has another or NULL ->mm. > >> > >> Recently kvm_async_page_present_sync() was added insedie the "use_mm" > >> section, but it seems that it doesn't need current->mm too. > >> > >> Signed-off-by: Oleg Nesterov > > > > Indeed, use/unuse_mm should only be necessary for copy_to/from_user etc. > > This is fine for s390, but it seems that x86 kvm_arch_async_page_not_present > > might call apf_put_user which might call copy_to_user, so this is not ok, I > > guess. > > wanted to say kvm_arch_async_page_not_present, but I have to correct myself. > x86 does the "page is there" in the cpu loop, not in the worker. The cpu look > d oes have a valid mm. So this patch should be also ok. Thanks ;) Btw, I forgot to mention this in the changelog, but > >> @@ -80,12 +80,10 @@ static void async_pf_execute(struct work_struct *work) > >> > >>might_sleep(); > >> > >> - use_mm(mm); > >>down_read(>mmap_sem); > >>get_user_pages(current, mm, addr, 1, 1, 0, NULL, NULL); > >>up_read(>mmap_sem); > >>kvm_async_page_present_sync(vcpu, apf); > >> - unuse_mm(mm); it can actually do get_user_pages(NULL, mm, addr, 1, 1, 0, NULL, NULL); "task" is only used to increment task_struct->xxx_flt. I don't think async_pf_execute() actually needs this (current is PF_WQ_WORKER after all), but I didn't dare to do another change in the code I can hardly understand. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 1/2] KVM: async_pf: kill the unnecessary use_mm/unuse_mm async_pf_execute()
On 04/22, Christian Borntraeger wrote: On 22/04/14 22:15, Christian Borntraeger wrote: On 21/04/14 15:25, Oleg Nesterov wrote: async_pf_execute() has no reasons to adopt apf-mm, gup(current, mm) should work just fine even if current has another or NULL -mm. Recently kvm_async_page_present_sync() was added insedie the use_mm section, but it seems that it doesn't need current-mm too. Signed-off-by: Oleg Nesterov o...@redhat.com Indeed, use/unuse_mm should only be necessary for copy_to/from_user etc. This is fine for s390, but it seems that x86 kvm_arch_async_page_not_present might call apf_put_user which might call copy_to_user, so this is not ok, I guess. wanted to say kvm_arch_async_page_not_present, but I have to correct myself. x86 does the page is there in the cpu loop, not in the worker. The cpu look d oes have a valid mm. So this patch should be also ok. Thanks ;) Btw, I forgot to mention this in the changelog, but @@ -80,12 +80,10 @@ static void async_pf_execute(struct work_struct *work) might_sleep(); - use_mm(mm); down_read(mm-mmap_sem); get_user_pages(current, mm, addr, 1, 1, 0, NULL, NULL); up_read(mm-mmap_sem); kvm_async_page_present_sync(vcpu, apf); - unuse_mm(mm); it can actually do get_user_pages(NULL, mm, addr, 1, 1, 0, NULL, NULL); task is only used to increment task_struct-xxx_flt. I don't think async_pf_execute() actually needs this (current is PF_WQ_WORKER after all), but I didn't dare to do another change in the code I can hardly understand. Oleg. -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 1/2] KVM: async_pf: kill the unnecessary use_mm/unuse_mm async_pf_execute()
On 22/04/14 22:15, Christian Borntraeger wrote: > On 21/04/14 15:25, Oleg Nesterov wrote: >> async_pf_execute() has no reasons to adopt apf->mm, gup(current, mm) >> should work just fine even if current has another or NULL ->mm. >> >> Recently kvm_async_page_present_sync() was added insedie the "use_mm" >> section, but it seems that it doesn't need current->mm too. >> >> Signed-off-by: Oleg Nesterov > > Indeed, use/unuse_mm should only be necessary for copy_to/from_user etc. > This is fine for s390, but it seems that x86 kvm_arch_async_page_not_present > might call apf_put_user which might call copy_to_user, so this is not ok, I > guess. wanted to say kvm_arch_async_page_not_present, but I have to correct myself. x86 does the "page is there" in the cpu loop, not in the worker. The cpu look d oes have a valid mm. So this patch should be also ok. > >> --- >> virt/kvm/async_pf.c |2 -- >> 1 files changed, 0 insertions(+), 2 deletions(-) >> >> diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c >> index 10df100..0ced4f3 100644 >> --- a/virt/kvm/async_pf.c >> +++ b/virt/kvm/async_pf.c >> @@ -80,12 +80,10 @@ static void async_pf_execute(struct work_struct *work) >> >> might_sleep(); >> >> -use_mm(mm); >> down_read(>mmap_sem); >> get_user_pages(current, mm, addr, 1, 1, 0, NULL, NULL); >> up_read(>mmap_sem); >> kvm_async_page_present_sync(vcpu, apf); >> -unuse_mm(mm); >> >> spin_lock(>async_pf.lock); >> list_add_tail(>link, >async_pf.done); >> > > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 1/2] KVM: async_pf: kill the unnecessary use_mm/unuse_mm async_pf_execute()
On 21/04/14 15:25, Oleg Nesterov wrote: > async_pf_execute() has no reasons to adopt apf->mm, gup(current, mm) > should work just fine even if current has another or NULL ->mm. > > Recently kvm_async_page_present_sync() was added insedie the "use_mm" > section, but it seems that it doesn't need current->mm too. > > Signed-off-by: Oleg Nesterov Indeed, use/unuse_mm should only be necessary for copy_to/from_user etc. This is fine for s390, but it seems that x86 kvm_arch_async_page_not_present might call apf_put_user which might call copy_to_user, so this is not ok, I guess. > --- > virt/kvm/async_pf.c |2 -- > 1 files changed, 0 insertions(+), 2 deletions(-) > > diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c > index 10df100..0ced4f3 100644 > --- a/virt/kvm/async_pf.c > +++ b/virt/kvm/async_pf.c > @@ -80,12 +80,10 @@ static void async_pf_execute(struct work_struct *work) > > might_sleep(); > > - use_mm(mm); > down_read(>mmap_sem); > get_user_pages(current, mm, addr, 1, 1, 0, NULL, NULL); > up_read(>mmap_sem); > kvm_async_page_present_sync(vcpu, apf); > - unuse_mm(mm); > > spin_lock(>async_pf.lock); > list_add_tail(>link, >async_pf.done); > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 1/2] KVM: async_pf: kill the unnecessary use_mm/unuse_mm async_pf_execute()
On 21/04/14 15:25, Oleg Nesterov wrote: async_pf_execute() has no reasons to adopt apf-mm, gup(current, mm) should work just fine even if current has another or NULL -mm. Recently kvm_async_page_present_sync() was added insedie the use_mm section, but it seems that it doesn't need current-mm too. Signed-off-by: Oleg Nesterov o...@redhat.com Indeed, use/unuse_mm should only be necessary for copy_to/from_user etc. This is fine for s390, but it seems that x86 kvm_arch_async_page_not_present might call apf_put_user which might call copy_to_user, so this is not ok, I guess. --- virt/kvm/async_pf.c |2 -- 1 files changed, 0 insertions(+), 2 deletions(-) diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c index 10df100..0ced4f3 100644 --- a/virt/kvm/async_pf.c +++ b/virt/kvm/async_pf.c @@ -80,12 +80,10 @@ static void async_pf_execute(struct work_struct *work) might_sleep(); - use_mm(mm); down_read(mm-mmap_sem); get_user_pages(current, mm, addr, 1, 1, 0, NULL, NULL); up_read(mm-mmap_sem); kvm_async_page_present_sync(vcpu, apf); - unuse_mm(mm); spin_lock(vcpu-async_pf.lock); list_add_tail(apf-link, vcpu-async_pf.done); -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 1/2] KVM: async_pf: kill the unnecessary use_mm/unuse_mm async_pf_execute()
On 22/04/14 22:15, Christian Borntraeger wrote: On 21/04/14 15:25, Oleg Nesterov wrote: async_pf_execute() has no reasons to adopt apf-mm, gup(current, mm) should work just fine even if current has another or NULL -mm. Recently kvm_async_page_present_sync() was added insedie the use_mm section, but it seems that it doesn't need current-mm too. Signed-off-by: Oleg Nesterov o...@redhat.com Indeed, use/unuse_mm should only be necessary for copy_to/from_user etc. This is fine for s390, but it seems that x86 kvm_arch_async_page_not_present might call apf_put_user which might call copy_to_user, so this is not ok, I guess. wanted to say kvm_arch_async_page_not_present, but I have to correct myself. x86 does the page is there in the cpu loop, not in the worker. The cpu look d oes have a valid mm. So this patch should be also ok. --- virt/kvm/async_pf.c |2 -- 1 files changed, 0 insertions(+), 2 deletions(-) diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c index 10df100..0ced4f3 100644 --- a/virt/kvm/async_pf.c +++ b/virt/kvm/async_pf.c @@ -80,12 +80,10 @@ static void async_pf_execute(struct work_struct *work) might_sleep(); -use_mm(mm); down_read(mm-mmap_sem); get_user_pages(current, mm, addr, 1, 1, 0, NULL, NULL); up_read(mm-mmap_sem); kvm_async_page_present_sync(vcpu, apf); -unuse_mm(mm); spin_lock(vcpu-async_pf.lock); list_add_tail(apf-link, vcpu-async_pf.done); -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
[PATCH 1/2] KVM: async_pf: kill the unnecessary use_mm/unuse_mm async_pf_execute()
async_pf_execute() has no reasons to adopt apf->mm, gup(current, mm) should work just fine even if current has another or NULL ->mm. Recently kvm_async_page_present_sync() was added insedie the "use_mm" section, but it seems that it doesn't need current->mm too. Signed-off-by: Oleg Nesterov --- virt/kvm/async_pf.c |2 -- 1 files changed, 0 insertions(+), 2 deletions(-) diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c index 10df100..0ced4f3 100644 --- a/virt/kvm/async_pf.c +++ b/virt/kvm/async_pf.c @@ -80,12 +80,10 @@ static void async_pf_execute(struct work_struct *work) might_sleep(); - use_mm(mm); down_read(>mmap_sem); get_user_pages(current, mm, addr, 1, 1, 0, NULL, NULL); up_read(>mmap_sem); kvm_async_page_present_sync(vcpu, apf); - unuse_mm(mm); spin_lock(>async_pf.lock); list_add_tail(>link, >async_pf.done); -- 1.5.5.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
[PATCH 1/2] KVM: async_pf: kill the unnecessary use_mm/unuse_mm async_pf_execute()
async_pf_execute() has no reasons to adopt apf-mm, gup(current, mm) should work just fine even if current has another or NULL -mm. Recently kvm_async_page_present_sync() was added insedie the use_mm section, but it seems that it doesn't need current-mm too. Signed-off-by: Oleg Nesterov o...@redhat.com --- virt/kvm/async_pf.c |2 -- 1 files changed, 0 insertions(+), 2 deletions(-) diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c index 10df100..0ced4f3 100644 --- a/virt/kvm/async_pf.c +++ b/virt/kvm/async_pf.c @@ -80,12 +80,10 @@ static void async_pf_execute(struct work_struct *work) might_sleep(); - use_mm(mm); down_read(mm-mmap_sem); get_user_pages(current, mm, addr, 1, 1, 0, NULL, NULL); up_read(mm-mmap_sem); kvm_async_page_present_sync(vcpu, apf); - unuse_mm(mm); spin_lock(vcpu-async_pf.lock); list_add_tail(apf-link, vcpu-async_pf.done); -- 1.5.5.1 -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
