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Allow to specify for vm_fault_quick_hold_pages() that nofault mode

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should be honored.

We must not sleep or acquire any MI VM locks if TDP_NOFAULTING is
specified.  On the other hand, there were some callers in the tree
which set TDP_NOFAULTING for larger scope than needed, I fixed the
code which I wrote, but I suspect that linuxkpi and out of tree drm
drivers might abuse this still.

So only enable the mode for vm_fault_quick_hold_pages() where
vm_fault_hold() is not called when specifically asked by user.  I
decided to use vm_prot_t flag to not change KPI.  Since number of
flags in vm_prot_t is limited, I reused the same flag which was
already consumed for vm_map_lookup().

Reported and tested by:	pho (as part of the larger patch)
Reviewed by:	markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D14825
This commit is contained in:
Konstantin Belousov 2018-03-26 16:31:12 +00:00
parent 6dd381416b
commit 8ec533d336
2 changed files with 14 additions and 1 deletions
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4
sys/vm/vm.h
View File

@ -80,7 +80,9 @@ typedef u_char vm_prot_t; /* protection codes */
#define VM_PROT_WRITE ((vm_prot_t) 0x02)
#define VM_PROT_EXECUTE ((vm_prot_t) 0x04)
#define VM_PROT_COPY ((vm_prot_t) 0x08) /* copy-on-read */
#define VM_PROT_FAULT_LOOKUP ((vm_prot_t) 0x010)
#define VM_PROT_PRIV_FLAG ((vm_prot_t) 0x10)
#define VM_PROT_FAULT_LOOKUP VM_PROT_PRIV_FLAG
#define VM_PROT_QUICK_NOFAULT VM_PROT_PRIV_FLAG /* same to save bits */
#define VM_PROT_ALL (VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE)
#define VM_PROT_RW (VM_PROT_READ|VM_PROT_WRITE)

11
sys/vm/vm_fault.c
View File

@ -1524,7 +1524,18 @@ vm_fault_quick_hold_pages(vm_map_t map, vm_offset_t addr, vm_size_t len,
* page was mapped at the specified virtual address or that
* mapping had insufficient permissions. Attempt to fault in
* and hold these pages.
*
* If vm_fault_disable_pagefaults() was called,
* i.e., TDP_NOFAULTING is set, we must not sleep nor
* acquire MD VM locks, which means we must not call
* vm_fault_hold(). Some (out of tree) callers mark
* too wide a code area with vm_fault_disable_pagefaults()
* already, use the VM_PROT_QUICK_NOFAULT flag to request
* the proper behaviour explicitly.
*/
if ((prot & VM_PROT_QUICK_NOFAULT) != 0 &&
(curthread->td_pflags & TDP_NOFAULTING) != 0)
goto error;
for (mp = ma, va = addr; va < end; mp++, va += PAGE_SIZE)
if (*mp == NULL && vm_fault_hold(map, va, prot,
VM_FAULT_NORMAL, mp) != KERN_SUCCESS)