On Wed, 2022-02-23 at 17:05 +1000, Nicholas Piggin wrote: > Excerpts from Haren Myneni's message of February 20, 2022 5:58 am: > > The VAS window may not be active if the system looses credits and > > the NX generates page fault when it receives request on unmap > > paste address. > > > > The kernel handles the fault by remap new paste address if the > > window is active again, Otherwise return the paste instruction > > failure if the executed instruction that caused the fault was > > a paste. > > Looks good, thanks for fixin the SIGBUS thing, was that my > fault? I vaguely remember writing some of this patch :P
Thanks for your reviews on all patches. No, it was my fault not handling the -EGAIN error. > > Thanks, > Nick > > > Signed-off-by: Nicholas Piggin <npig...@gmail.com> > > Signed-off-by: Haren Myneni <ha...@linux.ibm.com> > > --- > > arch/powerpc/include/asm/ppc-opcode.h | 2 + > > arch/powerpc/platforms/book3s/vas-api.c | 55 > > ++++++++++++++++++++++++- > > 2 files changed, 56 insertions(+), 1 deletion(-) > > > > diff --git a/arch/powerpc/include/asm/ppc-opcode.h > > b/arch/powerpc/include/asm/ppc-opcode.h > > index 9675303b724e..82f1f0041c6f 100644 > > --- a/arch/powerpc/include/asm/ppc-opcode.h > > +++ b/arch/powerpc/include/asm/ppc-opcode.h > > @@ -262,6 +262,8 @@ > > #define PPC_INST_MFSPR_PVR 0x7c1f42a6 > > #define PPC_INST_MFSPR_PVR_MASK 0xfc1ffffe > > #define PPC_INST_MTMSRD 0x7c000164 > > +#define PPC_INST_PASTE 0x7c20070d > > +#define PPC_INST_PASTE_MASK 0xfc2007ff > > #define PPC_INST_POPCNTB 0x7c0000f4 > > #define PPC_INST_POPCNTB_MASK 0xfc0007fe > > #define PPC_INST_RFEBB 0x4c000124 > > diff --git a/arch/powerpc/platforms/book3s/vas-api.c > > b/arch/powerpc/platforms/book3s/vas-api.c > > index f359e7b2bf90..f3e421511ea6 100644 > > --- a/arch/powerpc/platforms/book3s/vas-api.c > > +++ b/arch/powerpc/platforms/book3s/vas-api.c > > @@ -351,6 +351,41 @@ static int coproc_release(struct inode *inode, > > struct file *fp) > > return 0; > > } > > > > +/* > > + * If the executed instruction that caused the fault was a paste, > > then > > + * clear regs CR0[EQ], advance NIP, and return 0. Else return > > error code. > > + */ > > +static int do_fail_paste(void) > > +{ > > + struct pt_regs *regs = current->thread.regs; > > + u32 instword; > > + > > + if (WARN_ON_ONCE(!regs)) > > + return -EINVAL; > > + > > + if (WARN_ON_ONCE(!user_mode(regs))) > > + return -EINVAL; > > + > > + /* > > + * If we couldn't translate the instruction, the driver should > > + * return success without handling the fault, it will be > > retried > > + * or the instruction fetch will fault. > > + */ > > + if (get_user(instword, (u32 __user *)(regs->nip))) > > + return -EAGAIN; > > + > > + /* > > + * Not a paste instruction, driver may fail the fault. > > + */ > > + if ((instword & PPC_INST_PASTE_MASK) != PPC_INST_PASTE) > > + return -ENOENT; > > + > > + regs->ccr &= ~0xe0000000; /* Clear CR0[0-2] to fail paste */ > > + regs_add_return_ip(regs, 4); /* Emulate the paste */ > > + > > + return 0; > > +} > > + > > /* > > * This fault handler is invoked when the core generates page > > fault on > > * the paste address. Happens if the kernel closes window in > > hypervisor > > @@ -408,9 +443,27 @@ static vm_fault_t vas_mmap_fault(struct > > vm_fault *vmf) > > } > > mutex_unlock(&txwin->task_ref.mmap_mutex); > > > > - return VM_FAULT_SIGBUS; > > + /* > > + * Received this fault due to closing the actual window. > > + * It can happen during migration or lost credits. > > + * Since no mapping, return the paste instruction failure > > + * to the user space. > > + */ > > + ret = do_fail_paste(); > > + /* > > + * The user space can retry several times until success (needed > > + * for migration) or should fallback to SW compression or > > + * manage with the existing open windows if available. > > + * Looking at sysfs interface, it can determine whether these > > + * failures are coming during migration or core removal: > > + * nr_used_credits > nr_total_credits when lost credits > > + */ > > + if (!ret || (ret == -EAGAIN)) > > + return VM_FAULT_NOPAGE; > > > > + return VM_FAULT_SIGBUS; > > } > > + > > static const struct vm_operations_struct vas_vm_ops = { > > .fault = vas_mmap_fault, > > }; > > -- > > 2.27.0 > > > > > >