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source: trunk/hal/tsar_mips32/hal_gpt.c @ 3

Last change on this file since 3 was 1, checked in by alain, 8 years ago
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1	/*
2	* hal_gpt.c - implementation of the Generic Page Table API for TSAR-MIPS32
3	*
4	* Author Alain Greiner (2016)
5	*
6	* Copyright (c) UPMC Sorbonne Universites
7	*
8	* This file is part of ALMOS-MKH.
9	*
10	* ALMOS-MKH.is free software; you can redistribute it and/or modify it
11	* under the terms of the GNU General Public License as published by
12	* the Free Software Foundation; version 2.0 of the License.
13	*
14	* ALMOS-MKH.is distributed in the hope that it will be useful, but
15	* WITHOUT ANY WARRANTY; without even the implied warranty of
16	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17	* General Public License for more details.
18	*
19	* You should have received a copy of the GNU General Public License
20	* along with ALMOS-MKH.; if not, write to the Free Software Foundation,
21	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
22	*/
23
24	#include <hal_types.h>
25	#include <hal_gpt.h>
26	#include <hal_special.h>
27	#include <printk.h>
28	#include <bits.h>
29	#include <process.h>
30	#include <kmem.h>
31	#include <thread.h>
32	#include <cluster.h>
33	#include <ppm.h>
34	#include <page.h>
35
36	////////////////////////////////////////////////////////////////////////////////////////
37	// This define the masks for the TSAR MMU PTE attributes. (from TSAR MMU specification)
38	// the GPT masks are derived from the TSAR MMU PTE attributes
39	// in the TSAR specific hal_gpt_create() function.
40	////////////////////////////////////////////////////////////////////////////////////////
41
42	#define TSAR_MMU_PRESENT 0x80000000
43	#define TSAR_MMU_PTD1 0x40000000
44	#define TSAR_MMU_LOCAL 0x20000000
45	#define TSAR_MMU_REMOTE 0x10000000
46	#define TSAR_MMU_CACHABLE 0x08000000
47	#define TSAR_MMU_WRITABLE 0x04000000
48	#define TSAR_MMU_EXECUTABLE 0x02000000
49	#define TSAR_MMU_USER 0x01000000
50	#define TSAR_MMU_GLOBAL 0x00800000
51	#define TSAR_MMU_DIRTY 0x00400000
52
53	#define TSAR_MMU_COW 0x00000001
54	#define TSAR_MMU_SWAP 0x00000004
55	#define TSAR_MMU_LOCKED 0x00000008
56
57	////////////////////////////////////////////////////////////////////////////////////////
58	// TSAR MMU related macros (from the TSAR MMU specification)
59	// - IX1 on 11 bits
60	// - IX2 on 9 bits
61	// - PPN on 28 bits
62	////////////////////////////////////////////////////////////////////////////////////////
63
64	#define TSAR_MMU_IX1_WIDTH 11
65	#define TSAR_MMU_IX2_WIDTH 9
66	#define TSAR_MMU_PPN_WIDTH 28
67
68	#define TSAR_MMU_IX1_FROM_VPN( vpn ) ((vpn >> 9) & 0x7FF)
69	#define TSAR_MMU_IX2_FROM_VPN( vpn ) (vpn & 0x1FF)
70
71	#define TSAR_MMU_PTBA_FROM_PTE1( pte1 ) (pte1 & 0xFFFFFFF)
72	#define TSAR_MMU_PPN_FROM_PTE1( pte1 ) ((pte1 & 0x7FFFF)<<9)
73	#define TSAR_MMU_ATTR_FROM_PTE1( pte1 ) (pte1 & 0xFFC00000)
74
75	#define TSAR_MMU_PPN_FROM_PTE2( pte2 ) (pte2 & 0x0FFFFFFF)
76	#define TSAR_MMU_ATTR_FROM_PTE2( pte2 ) (pte2 & 0xFFC000FF)
77
78	/****************************************************************************************
79	* These global variables defines the masks for the Generic Page Table Entry attributes,
80	* and must be defined in all GPT implementation.
81	***************************************************************************************/
82
83	uint32_t GPT_MAPPED;
84	uint32_t GPT_SMALL;
85	uint32_t GPT_READABLE;
86	uint32_t GPT_WRITABLE;
87	uint32_t GPT_EXECUTABLE;
88	uint32_t GPT_CACHABLE;
89	uint32_t GPT_USER;
90	uint32_t GPT_DIRTY;
91	uint32_t GPT_ACCESSED;
92	uint32_t GPT_GLOBAL;
93	uint32_t GPT_COW;
94	uint32_t GPT_SWAP;
95	uint32_t GPT_LOCKED;
96
97	/////////////////////////////////////
98	error_t hal_gpt_create( gpt_t * gpt )
99	{
100	page_t * page;
101
102	// check page size
103	if( CONFIG_PPM_PAGE_SIZE != 4096 );
104	{
105	printk("\n[PANIC] in %s : For TSAR, the page must be 4 Kbytes\n", __FUNCTION__ );
106	hal_core_sleep();
107	}
108
109	// allocates 2 physical pages for PT1
110	kmem_req_t req;
111	req.type = KMEM_PAGE;
112	req.size = 1; // 2 small pages
113	req.flags = AF_KERNEL \| AF_ZERO;
114	page = (page_t *)kmem_alloc( &req );
115
116	if( page == NULL )
117	{
118	printk("\n[ERROR] in %s : cannot allocate physical memory for PT1\n", __FUNCTION__ );
119	return ENOMEM;
120	}
121
122	// initialize generic page table descriptor
123	gpt->ptr = ppm_page2base( page );
124	gpt->ppn = ppm_page2ppn( page );
125	gpt->page = page;
126
127	// initialize PTE entries attributes masks
128	GPT_MAPPED = TSAR_MMU_PRESENT;
129	GPT_SMALL = TSAR_MMU_PTD1;
130	GPT_READABLE = TSAR_MMU_PRESENT;
131	GPT_WRITABLE = TSAR_MMU_WRITABLE;
132	GPT_EXECUTABLE = TSAR_MMU_EXECUTABLE;
133	GPT_CACHABLE = TSAR_MMU_CACHABLE;
134	GPT_USER = TSAR_MMU_USER;
135	GPT_DIRTY = TSAR_MMU_DIRTY;
136	GPT_ACCESSED = TSAR_MMU_LOCAL \| TSAR_MMU_REMOTE;
137	GPT_GLOBAL = TSAR_MMU_GLOBAL;
138	GPT_COW = TSAR_MMU_COW;
139	GPT_SWAP = TSAR_MMU_SWAP;
140	GPT_LOCKED = TSAR_MMU_LOCKED;
141
142	return 0;
143	} // end hal_gpt_create()
144
145
146	///////////////////////////////////
147	void hal_gpt_destroy( gpt_t * gpt )
148	{
149	uint32_t ix1;
150	uint32_t ix2;
151	uint32_t * pt1;
152	uint32_t pte1;
153	ppn_t pt2_ppn;
154	uint32_t * pt2;
155	uint32_t attr;
156	vpn_t vpn;
157	kmem_req_t req;
158	bool_t is_ref;
159
160	// get pointer on calling process
161	process_t * process = CURRENT_THREAD->process;
162
163	// compute is_ref
164	is_ref = process->is_ref;
165
166	// get pointer on PT1
167	pt1 = (uint32_t *)gpt->ptr;
168
169	// scan the PT1
170	for( ix1 = 0 ; ix1 < 2048 ; ix1++ )
171	{
172	pte1 = pt1[ix1];
173	if( (pte1 & GPT_MAPPED) != 0 ) // PTE1 valid
174	{
175	if( (pte1 & GPT_SMALL) == 0 ) // BIG page
176	{
177	if( (pte1 & GPT_USER) != 0 )
178	{
179	// warning message
180	printk("\n[WARNING] in %s : found an USER BIG page / ix1 = %d\n",
181	__FUNCTION__ , ix1 );
182
183	// release the big physical page if reference cluster
184	if( is_ref )
185	{
186	vpn = (vpn_t)(ix1 << TSAR_MMU_IX2_WIDTH);
187	hal_gpt_reset_pte( gpt , vpn );
188	}
189	}
190	}
191	else // SMALL page
192	{
193	// get pointer on PT2
194	pt2_ppn = TSAR_MMU_PTBA_FROM_PTE1( pte1 );
195	pt2 = ppm_ppn2base( pt2_ppn );
196
197	// scan the PT2 to release all entries VALID and USER if reference cluster
198	if( is_ref )
199	{
200	for( ix2 = 0 ; ix2 < 512 ; ix2++ )
201	{
202	attr = TSAR_MMU_ATTR_FROM_PTE2( pt2[2 * ix2] );
203	if( ((attr & GPT_MAPPED) != 0 ) && ((attr & GPT_USER) != 0) )
204	{
205	// release the physical page
206	vpn = (vpn_t)((ix1 << TSAR_MMU_IX2_WIDTH) \| ix2);
207	hal_gpt_reset_pte( gpt , vpn );
208	}
209	}
210	}
211
212	// release the PT2
213	req.type = KMEM_PAGE;
214	req.ptr = ppm_base2page( pt2 );
215	kmem_free( &req );
216	}
217	}
218	}
219
220	// release the PT1
221	req.type = KMEM_PAGE;
222	req.ptr = ppm_base2page( pt1 );
223	kmem_free( &req );
224
225	} // end hal_gpt_destroy()
226
227	/////////////////////////////////
228	void hal_gpt_print( gpt_t * gpt )
229	{
230	uint32_t ix1;
231	uint32_t ix2;
232	uint32_t * pt1;
233	uint32_t pte1;
234	ppn_t pt2_ppn;
235	uint32_t * pt2;
236	uint32_t pte2_attr;
237	ppn_t pte2_ppn;
238
239	printk("* Page Table for process %x in cluster %x *\n",
240	CURRENT_PROCESS->pid , local_cxy );
241
242	pt1 = (uint32_t *)gpt->ptr;
243
244	// scan the PT1
245	for( ix1 = 0 ; ix1 < 2048 ; ix1++ )
246	{
247	pte1 = pt1[ix1];
248	if( (pte1 & GPT_MAPPED) != 0 )
249	{
250	if( (pte1 & GPT_SMALL) == 0 ) // BIG page
251	{
252	printk(" - BIG : pt1[%d] = %x\n", ix1 , pte1 );
253	}
254	else // SMALL pages
255	{
256	pt2_ppn = TSAR_MMU_PTBA_FROM_PTE1( pte1 );
257	pt2 = ppm_ppn2base( pt2_ppn );
258
259	// scan the PT2
260	for( ix2 = 0 ; ix2 < 512 ; ix2++ )
261	{
262	pte2_attr = TSAR_MMU_ATTR_FROM_PTE2( pt2[2 * ix2] );
263	pte2_ppn = TSAR_MMU_PPN_FROM_PTE2( pt2[2 * ix2 + 1] );
264	if( (pte2_attr & GPT_MAPPED) != 0 )
265	{
266	printk(" - SMALL : pt1[%d] = %x / pt2[%d] / pt2[%d]\n",
267	ix1 , pt1[ix1] , 2ix2 , pte2_attr , 2ix2+1 , pte2_ppn );
268	}
269	}
270	}
271	}
272	}
273	} // end hal_gpt_print()
274
275
276	///////////////////////////////////////
277	error_t hal_gpt_set_pte( gpt_t * gpt,
278	vpn_t vpn,
279	ppn_t ppn,
280	uint32_t attr )
281	{
282	uint32_t * pt1; // virtual base addres of PT1
283	volatile uint32_t * pte1_ptr; // pointer on PT1 entry
284	uint32_t pte1; // PT1 entry value
285
286	ppn_t pt2_ppn; // PPN of PT2
287	uint32_t * pt2; // virtual base address of PT2
288
289	uint32_t small; // requested PTE is for a small page
290	bool_t atomic; //
291	page_t * page; // pointer on new physical page descriptor
292
293	uint32_t ix1; // index in PT1
294	uint32_t ix2; // index in PT2
295
296	// compute indexes in PT1 and PT2
297	ix1 = TSAR_MMU_IX1_FROM_VPN( vpn );
298	ix2 = TSAR_MMU_IX2_FROM_VPN( vpn );
299
300	pt1 = gpt->ptr;
301	small = (attr & GPT_SMALL);
302
303	// get PT1 entry value
304	pte1_ptr = &pt1[ix1];
305	pte1 = *pte1_ptr;
306
307	// Big pages (PTE1) are only set for the kernel vsegs, in the kernel init phase.
308	// There is no risk of concurrent access.
309	if( small == 0 )
310	{
311	if( (pte1 != 0) \|\| (attr & GPT_COW) )
312	{
313	printk("\n[ERROR] in %s : set a big page in a mapped PT1 entry / PT1[%d] = %x\n",
314	__FUNCTION__ , ix1 , pte1 );
315	return EINVAL;
316	}
317
318	// set the PTE1
319	*pte1_ptr = attr \| (ppn >> 9);
320	hal_wbflush();
321	return 0;
322	}
323
324	// From this point, the requested PTE is a PTE2 (small page)
325
326	if( (pte1 & GPT_MAPPED) == 0 ) // the PT1 entry is not valid
327	{
328	// allocate one physical page for the PT2
329	kmem_req_t req;
330	req.type = KMEM_PAGE;
331	req.size = 0; // 1 small page
332	req.flags = AF_KERNEL \| AF_ZERO;
333	page = (page_t *)kmem_alloc( &req );
334	if( page == NULL )
335	{
336	printk("\n[ERROR] in %s : try to set a small page but cannot allocate PT2\n",
337	__FUNCTION__ );
338	return ENOMEM;
339	}
340	pt2_ppn = ppm_page2ppn( page );
341	pt2 = ppm_page2base( page );
342
343	// try to atomicaly set a PTD1 in the PT1 entry
344	do
345	{
346	atomic = hal_atomic_cas( (void*)pte1, 0 ,
347	TSAR_MMU_PRESENT \| TSAR_MMU_PTD1 \| pt2_ppn );
348	}
349	while( (atomic == false) && (*pte1_ptr == 0) );
350
351	if( atomic == false ) // the mapping has been done by another thread !!!
352	{
353	// release the allocated page
354	ppm_free_pages( page );
355
356	// read PT1 entry again
357	pte1 = *pte1_ptr;
358
359	// compute PPN of PT2 base
360	pt2_ppn = TSAR_MMU_PTBA_FROM_PTE1( pte1 );
361
362	// compute pointer on PT2 base
363	pt2 = (uint32_t*)ppm_ppn2base( pt2_ppn );
364	}
365	}
366	else // The PT1 entry is valid
367	{
368	// This valid entry must be a PTD1
369	if( (pte1 & GPT_SMALL) == 0 )
370	{
371	printk("\n[ERROR] in %s : set a small page in a big PT1 entry / PT1[%d] = %x\n",
372	__FUNCTION__ , ix1 , pte1 );
373	return EINVAL;
374	}
375
376	// compute PPN of PT2 base
377	pt2_ppn = TSAR_MMU_PTBA_FROM_PTE1( pte1 );
378
379	// compute pointer on PT2 base
380	pt2 = (uint32_t*)ppm_ppn2base( pt2_ppn );
381	}
382
383	// set PTE2 in this order
384	pt2[2 * ix2 + 1] = ppn;
385	hal_wbflush();
386	pt2[2 * ix2] = attr;
387	hal_wbflush();
388
389	return 0;
390	} // end of hal_gpt_set_pte()
391
392	/////////////////////////////////////
393	void hal_gpt_get_pte( gpt_t * gpt,
394	vpn_t vpn,
395	uint32_t * attr,
396	ppn_t * ppn )
397	{
398	uint32_t * pt1;
399	uint32_t pte1;
400
401	uint32_t * pt2;
402	ppn_t pt2_ppn;
403
404	uint32_t ix1 = TSAR_MMU_IX1_FROM_VPN( vpn );
405	uint32_t ix2 = TSAR_MMU_IX2_FROM_VPN( vpn );
406
407	// get PTE1 value
408	pt1 = gpt->ptr;
409	pte1 = pt1[ix1];
410
411	if( (pte1 & GPT_MAPPED) == 0 ) // PT1 entry not present
412	{
413	*attr = 0;
414	*ppn = 0;
415	}
416
417	if( (pte1 & GPT_SMALL) == 0 ) // it's a PTE1
418	{
419	*attr = TSAR_MMU_ATTR_FROM_PTE1( pte1 );
420	*ppn = TSAR_MMU_PPN_FROM_PTE1( pte1 ) \| (vpn & ((1<<TSAR_MMU_IX2_WIDTH)-1));
421	}
422	else // it's a PTD1
423	{
424	// compute PT2 base address
425	pt2_ppn = TSAR_MMU_PTBA_FROM_PTE1( pte1 );
426	pt2 = (uint32_t*)ppm_ppn2base( pt2_ppn );
427
428	ppn = pt2[2ix2+1] & ((1<<TSAR_MMU_PPN_WIDTH)-1);
429	attr = pt2[2ix2];
430	}
431	} // end hal_gpt_get_pte()
432
433	////////////////////////////////////
434	void hal_gpt_reset_pte( gpt_t * gpt,
435	vpn_t vpn )
436	{
437	uint32_t * pt1; // PT1 base address
438	uint32_t pte1; // PT1 entry value
439
440	ppn_t pt2_ppn; // PPN of PT2
441	uint32_t * pt2; // PT2 base address
442
443	ppn_t ppn; // PPN of page to be released
444
445	kmem_req_t req;
446
447	uint32_t ix1 = TSAR_MMU_IX1_FROM_VPN( vpn );
448	uint32_t ix2 = TSAR_MMU_IX2_FROM_VPN( vpn );
449
450	// get PTE1 value
451	pt1 = gpt->ptr;
452	pte1 = pt1[ix1];
453
454	if( (pte1 & GPT_MAPPED) == 0 ) // PT1 entry not present
455	{
456	return;
457	}
458
459	if( (pte1 & GPT_SMALL) == 0 ) // it's a PTE1
460	{
461	// get PPN
462	ppn = TSAR_MMU_PPN_FROM_PTE1( pte1 );
463
464	// unmap the big page
465	pt1[ix1] = 0;
466	hal_wbflush();
467
468	// releases the big page
469	req.type = KMEM_PAGE;
470	req.size = 9;
471	req.ptr = (void*)(ppn << CONFIG_PPM_PAGE_SHIFT);
472	kmem_free( &req );
473
474	return;
475	}
476	else // it's a PTD1
477	{
478	// compute PT2 base address
479	pt2_ppn = TSAR_MMU_PTBA_FROM_PTE1( pte1 );
480	pt2 = (uint32_t*)ppm_ppn2base( pt2_ppn );
481
482	// get PPN
483	ppn = TSAR_MMU_PPN_FROM_PTE2( pt2[2*ix2+1] );
484
485	// unmap the small page
486	pt2[2*ix2] = 0;
487	hal_wbflush();
488	pt2[2*ix2+1] = 0;
489	hal_wbflush();
490
491	// releases the small page
492	req.type = KMEM_PAGE;
493	req.size = 0;
494	req.ptr = (void*)(ppn << CONFIG_PPM_PAGE_SHIFT);
495	kmem_free( &req );
496
497	return;
498	}
499	} // end hal_gpt_reset_pte()
500
501	//////////////////////////////////////
502	error_t hal_gpt_lock_pte( gpt_t * gpt,
503	vpn_t vpn )
504	{
505	uint32_t * pt1; // PT1 base address
506	volatile uint32_t * pte1_ptr; // address of PT1 entry
507	uint32_t pte1; // value of PT1 entry
508
509	uint32_t * pt2; // PT2 base address
510	ppn_t pt2_ppn; // PPN of PT2 page if missing PT2
511	volatile uint32_t * pte2_ptr; // address of PT2 entry
512
513	uint32_t attr;
514	bool_t atomic;
515	page_t * page;
516
517	uint32_t ix1 = TSAR_MMU_IX1_FROM_VPN( vpn ); // index in PT1
518	uint32_t ix2 = TSAR_MMU_IX2_FROM_VPN( vpn ); // index in PT2
519
520	// get the PTE1 value
521	pt1 = gpt->ptr;
522	pte1_ptr = &pt1[ix1];
523	pte1 = *pte1_ptr;
524
525	// If present, the page must be small
526	if( ((pte1 & GPT_MAPPED) != 0) && ((pte1 & GPT_SMALL) == 0) )
527	{
528	printk("\n[ERROR] in %s : try to lock a big page / PT1[%d] = %x\n",
529	__FUNCTION__ , ix1 , pte1 );
530	return EINVAL;
531	}
532
533	if( (pte1 & GPT_MAPPED) == 0 ) // missing PT1 entry
534	{
535	// allocate one physical page for PT2
536	kmem_req_t req;
537	req.type = KMEM_PAGE;
538	req.size = 0; // 1 small page
539	req.flags = AF_KERNEL \| AF_ZERO;
540	page = (page_t *)kmem_alloc( &req );
541	if( page == NULL )
542	{
543	printk("\n[ERROR] in %s : try to set a small page but cannot allocate PT2\n",
544	__FUNCTION__ );
545	return ENOMEM;
546	}
547	pt2_ppn = ppm_page2ppn( page );
548	pt2 = ppm_page2base( page );
549
550	// try to set the PT1 entry
551	do
552	{
553	atomic = hal_atomic_cas( (void*)pte1_ptr , 0 ,
554	TSAR_MMU_PRESENT \| TSAR_MMU_PTD1 \| pt2_ppn );
555	}
556	while( (atomic == false) && (*pte1_ptr == 0) );
557
558	if( atomic == false ) // missing PT2 has been allocate by another core
559	{
560	// release the allocated page
561	ppm_free_pages( page );
562
563	// read again the PTE1
564	pte1 = *pte1_ptr;
565
566	// get the PT2 base address
567	pt2_ppn = TSAR_MMU_PPN_FROM_PTE1( pte1 );
568	pt2 = (uint32_t*)ppm_ppn2base( pt2_ppn );
569	}
570	}
571	else
572	{
573	// This valid entry must be a PTD1
574	if( (pte1 & GPT_SMALL) == 0 )
575	{
576	printk("\n[ERROR] in %s : set a small page in a big PT1 entry / PT1[%d] = %x\n",
577	__FUNCTION__ , ix1 , pte1 );
578	return EINVAL;
579	}
580
581	// compute PPN of PT2 base
582	pt2_ppn = TSAR_MMU_PTBA_FROM_PTE1( pte1 );
583
584	// compute pointer on PT2 base
585	pt2 = (uint32_t*)ppm_ppn2base( pt2_ppn );
586	}
587
588	// from here we have the PT2 pointer
589
590	// compute pointer on PTE2
591	pte2_ptr = &pt2[2 * ix2];
592
593	// try to atomically lock the PTE2 until success
594	do
595	{
596	// busy waiting until GPT_LOCK == 0
597	do
598	{
599	attr = *pte2_ptr;
600	hal_rdbar();
601	}
602	while( (attr & GPT_LOCKED) != 0 );
603
604	// try to set the GPT_LOCK wit a CAS
605	atomic = hal_atomic_cas( (void*)pte2_ptr, attr , (attr \| GPT_LOCKED) );
606	}
607	while( atomic == 0 );
608
609	return 0;
610	} // end hal_gpt_lock_pte()
611
612	////////////////////////////////////////
613	error_t hal_gpt_unlock_pte( gpt_t * gpt,
614	vpn_t vpn )
615	{
616	uint32_t * pt1; // PT1 base address
617	uint32_t pte1; // value of PT1 entry
618
619	uint32_t * pt2; // PT2 base address
620	ppn_t pt2_ppn; // PPN of PT2 page if missing PT2
621	uint32_t * pte2_ptr; // address of PT2 entry
622
623	uint32_t attr; // PTE2 attribute
624
625	// compute indexes in P1 and PT2
626	uint32_t ix1 = TSAR_MMU_IX1_FROM_VPN( vpn ); // index in PT1
627	uint32_t ix2 = TSAR_MMU_IX2_FROM_VPN( vpn ); // index in PT2
628
629	// get pointer on PT1 base
630	pt1 = (uint32_t*)gpt->ptr;
631
632	// get PTE1
633	pte1 = pt1[ix1];
634
635	// check PTE1 present and small page
636	if( ((pte1 & GPT_MAPPED) == 0) \|\| ((pte1 & GPT_SMALL) == 0) )
637	{
638	printk("\n[ERROR] in %s : try to unlock a big or undefined page / PT1[%d] = %x\n",
639	__FUNCTION__ , ix1 , pte1 );
640	return EINVAL;
641	}
642
643	// get pointer on PT2 base
644	pt2_ppn = TSAR_MMU_PPN_FROM_PTE1( pte1 );
645	pt2 = ppm_ppn2base( pt2_ppn );
646
647	// get pointer on PTE2
648	pte2_ptr = &pt2[2 * ix2];
649
650	// get PTE2_ATTR
651	attr = *pte2_ptr;
652
653	// check PTE2 present and locked
654	if( ((attr & GPT_MAPPED) == 0) \|\| ((attr & GPT_LOCKED) == 0) );
655	{
656	printk("\n[ERROR] in %s : try to unlock an undefined page / PT1[%d] = %x\n",
657	__FUNCTION__ , ix1 , pte1 );
658	return EINVAL;
659	}
660
661	// reset GPT_LOCK
662	*pte2_ptr = attr & !GPT_LOCKED;
663
664	return 0;
665	} // end hal_gpt_unlock_pte()
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