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powerpc/vas: Return paste instruction failure if no active window 

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 <npiggin@gmail.com>
Signed-off-by: Haren Myneni <haren@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/492b9aefd593061d51dda67ee4d2fc449c000dce.camel@linux.ibm.com
This commit is contained in:
Haren Myneni 2022-02-28 17:13:15 -08:00 committed by Michael Ellerman
parent 1fe3a33ba0
commit b5c63d90cc
2 changed files with 56 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/powerpc/include/asm/ppc-opcode.h
View File

@ -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

54
arch/powerpc/platforms/book3s/vas-api.c
View File

@ -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
@ -364,6 +399,7 @@ static vm_fault_t vas_mmap_fault(struct vm_fault *vmf)
struct vas_window *txwin;
vm_fault_t fault;
u64 paste_addr;
int ret;
/*
* window is not opened. Shouldn't expect this error.
@ -408,6 +444,24 @@ static vm_fault_t vas_mmap_fault(struct vm_fault *vmf)
}
mutex_unlock(&txwin->task_ref.mmap_mutex);
/*
* 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;
}