Excerpts from Haren Myneni's message of January 22, 2022 5:59 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.
>
> 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 | 47 ++++++++++++++++++++++++-
> 2 files changed, 48 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/include/asm/ppc-opcode.h
> b/arch/powerpc/include/asm/ppc-opcode.h
> index efad07081cc0..fe2a69206588 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 5ceba75c13eb..2ffd34bc4032 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;
We say this, and yet the caller seems to SIGBUS us on this return
value.
> +
> + /*
> + * 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); /* Skip the paste */
Maybe instead of 'Skip the paste' the comment should be 'Emulated the
paste'.
> +
> + return 0;
> +}
> +
> /*
> * This fault handler is invoked when the VAS/NX generates page fault on
> * the paste address. Happens if the kernel closes window in hypervisor
> @@ -403,9 +438,19 @@ 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();
> + if (!ret)
> + return VM_FAULT_NOPAGE;
if (!ret || ret == -EAGAIN)
?
Thanks,
Nick
>
> + return VM_FAULT_SIGBUS;
> }
> +
> static const struct vm_operations_struct vas_vm_ops = {
> .fault = vas_mmap_fault,
> };
> --
> 2.27.0
>
>
>
