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Date: Tue, 9 Jul 2013 18:23:46 +0300
From: Gleb Natapov <gleb@...hat.com>
To: Dominik Dingel <dingel@...ux.vnet.ibm.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Christian Borntraeger <borntraeger@...ibm.com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Martin Schwidefsky <schwidefsky@...ibm.com>,
Cornelia Huck <cornelia.huck@...ibm.com>,
Xiantao Zhang <xiantao.zhang@...el.com>,
Alexander Graf <agraf@...e.de>,
Christoffer Dall <christoffer.dall@...aro.org>,
Marc Zyngier <marc.zyngier@....com>,
Ralf Baechle <ralf@...ux-mips.org>, kvm@...r.kernel.org,
linux-s390@...r.kernel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] PF: Add FAULT_FLAG_RETRY_NOWAIT for guest fault
On Tue, Jul 09, 2013 at 03:56:44PM +0200, Dominik Dingel wrote:
> In case of a fault retry exit sie64() with gmap_fault indication for the
> running thread set. This makes it possible to handle async page faults
> without the need for mm notifiers.
>
> Based on a patch from Martin Schwidefsky.
>
For that we will obviously need Christian and Cornelia ACKs. Or it can
go in via S390 tree.
> Signed-off-by: Dominik Dingel <dingel@...ux.vnet.ibm.com>
> ---
> arch/s390/include/asm/pgtable.h | 2 ++
> arch/s390/include/asm/processor.h | 1 +
> arch/s390/kvm/kvm-s390.c | 13 +++++++++++++
> arch/s390/mm/fault.c | 26 ++++++++++++++++++++++----
> 4 files changed, 38 insertions(+), 4 deletions(-)
>
> diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
> index 0ea4e59..4a4cc64 100644
> --- a/arch/s390/include/asm/pgtable.h
> +++ b/arch/s390/include/asm/pgtable.h
> @@ -740,6 +740,7 @@ static inline void pgste_set_pte(pte_t *ptep, pte_t entry)
> * @table: pointer to the page directory
> * @asce: address space control element for gmap page table
> * @crst_list: list of all crst tables used in the guest address space
> + * @pfault_enabled: defines if pfaults are applicable for the guest
> */
> struct gmap {
> struct list_head list;
> @@ -748,6 +749,7 @@ struct gmap {
> unsigned long asce;
> void *private;
> struct list_head crst_list;
> + unsigned long pfault_enabled;
> };
>
> /**
> diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h
> index 6b49987..4fa96ca 100644
> --- a/arch/s390/include/asm/processor.h
> +++ b/arch/s390/include/asm/processor.h
> @@ -77,6 +77,7 @@ struct thread_struct {
> unsigned long ksp; /* kernel stack pointer */
> mm_segment_t mm_segment;
> unsigned long gmap_addr; /* address of last gmap fault. */
> + unsigned int gmap_pfault; /* signal of a pending guest pfault */
> struct per_regs per_user; /* User specified PER registers */
> struct per_event per_event; /* Cause of the last PER trap */
> unsigned long per_flags; /* Flags to control debug behavior */
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index ba694d2..702daca 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -682,6 +682,15 @@ static int kvm_s390_handle_requests(struct kvm_vcpu *vcpu)
> return 0;
> }
>
> +static void kvm_arch_fault_in_sync(struct kvm_vcpu *vcpu)
> +{
> + hva_t fault = gmap_fault(current->thread.gmap_addr, vcpu->arch.gmap);
> + struct mm_struct *mm = current->mm;
> + down_read(&mm->mmap_sem);
> + get_user_pages(current, mm, fault, 1, 1, 0, NULL, NULL);
> + up_read(&mm->mmap_sem);
> +}
> +
> static int __vcpu_run(struct kvm_vcpu *vcpu)
> {
> int rc;
> @@ -715,6 +724,10 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
> if (rc < 0) {
> if (kvm_is_ucontrol(vcpu->kvm)) {
> rc = SIE_INTERCEPT_UCONTROL;
> + } else if (current->thread.gmap_pfault) {
> + kvm_arch_fault_in_sync(vcpu);
> + current->thread.gmap_pfault = 0;
> + rc = 0;
> } else {
> VCPU_EVENT(vcpu, 3, "%s", "fault in sie instruction");
> trace_kvm_s390_sie_fault(vcpu);
> diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
> index 047c3e4..7d4c4b1 100644
> --- a/arch/s390/mm/fault.c
> +++ b/arch/s390/mm/fault.c
> @@ -50,6 +50,7 @@
> #define VM_FAULT_BADMAP 0x020000
> #define VM_FAULT_BADACCESS 0x040000
> #define VM_FAULT_SIGNAL 0x080000
> +#define VM_FAULT_PFAULT 0x100000
>
> static unsigned long store_indication __read_mostly;
>
> @@ -232,6 +233,7 @@ static noinline void do_fault_error(struct pt_regs *regs, int fault)
> return;
> }
> case VM_FAULT_BADCONTEXT:
> + case VM_FAULT_PFAULT:
> do_no_context(regs);
> break;
> case VM_FAULT_SIGNAL:
> @@ -269,6 +271,9 @@ static noinline void do_fault_error(struct pt_regs *regs, int fault)
> */
> static inline int do_exception(struct pt_regs *regs, int access)
> {
> +#ifdef CONFIG_PGSTE
> + struct gmap *gmap;
> +#endif
> struct task_struct *tsk;
> struct mm_struct *mm;
> struct vm_area_struct *vma;
> @@ -307,9 +312,10 @@ static inline int do_exception(struct pt_regs *regs, int access)
> down_read(&mm->mmap_sem);
>
> #ifdef CONFIG_PGSTE
> - if ((current->flags & PF_VCPU) && S390_lowcore.gmap) {
> - address = __gmap_fault(address,
> - (struct gmap *) S390_lowcore.gmap);
> + gmap = (struct gmap *)
> + ((current->flags & PF_VCPU) ? S390_lowcore.gmap : 0);
> + if (gmap) {
> + address = __gmap_fault(address, gmap);
> if (address == -EFAULT) {
> fault = VM_FAULT_BADMAP;
> goto out_up;
> @@ -318,6 +324,8 @@ static inline int do_exception(struct pt_regs *regs, int access)
> fault = VM_FAULT_OOM;
> goto out_up;
> }
> + if (test_bit(1, &gmap->pfault_enabled))
> + flags |= FAULT_FLAG_RETRY_NOWAIT;
> }
> #endif
>
> @@ -374,9 +382,19 @@ retry:
> regs, address);
> }
> if (fault & VM_FAULT_RETRY) {
> +#ifdef CONFIG_PGSTE
> + if (gmap && (flags & FAULT_FLAG_RETRY_NOWAIT)) {
> + /* FAULT_FLAG_RETRY_NOWAIT has been set,
> + * mmap_sem has not been released */
> + current->thread.gmap_pfault = 1;
> + fault = VM_FAULT_PFAULT;
> + goto out_up;
> + }
> +#endif
> /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
> * of starvation. */
> - flags &= ~FAULT_FLAG_ALLOW_RETRY;
> + flags &= ~(FAULT_FLAG_ALLOW_RETRY |
> + FAULT_FLAG_RETRY_NOWAIT);
> flags |= FAULT_FLAG_TRIED;
> down_read(&mm->mmap_sem);
> goto retry;
> --
> 1.8.2.2
--
Gleb.
--
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