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use NULL not 0 for pointer values in kern
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/*	$OpenBSD: vfs_biomem.c,v 1.51 2021/10/24 00:02:25 jsg Exp $ */

/*
 * Copyright (c) 2007 Artur Grabowski <art@openbsd.org>
 * Copyright (c) 2012-2016,2019 Bob Beck <beck@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */


#include <sys/param.h>
#include <sys/systm.h>
#include <sys/buf.h>
#include <sys/pool.h>
#include <sys/proc.h>		/* XXX for atomic */
#include <sys/mount.h>

#include <uvm/uvm_extern.h>

vaddr_t buf_kva_start, buf_kva_end;
int buf_needva;
TAILQ_HEAD(,buf) buf_valist;

extern struct bcachestats bcstats;

vaddr_t buf_unmap(struct buf *);

void
buf_mem_init(vsize_t size)
{
	TAILQ_INIT(&buf_valist);

	buf_kva_start = vm_map_min(kernel_map);
	if (uvm_map(kernel_map, &buf_kva_start, size, NULL,
	    UVM_UNKNOWN_OFFSET, PAGE_SIZE, UVM_MAPFLAG(PROT_NONE,
	    PROT_NONE, MAP_INHERIT_NONE, MADV_NORMAL, 0)))
		panic("%s: can't reserve VM for buffers", __func__);
	buf_kva_end = buf_kva_start + size;

	/* Contiguous mapping */
	bcstats.kvaslots = bcstats.kvaslots_avail = size / MAXPHYS;
}

/*
 * buf_acquire and buf_release manage the kvm mappings of buffers.
 */
void
buf_acquire(struct buf *bp)
{
	KASSERT((bp->b_flags & B_BUSY) == 0);
	splassert(IPL_BIO);
	/*
	 * Busy before waiting for kvm.
	 */
	SET(bp->b_flags, B_BUSY);
	buf_map(bp);
}

/*
 * Acquire a buf but do not map it. Preserve any mapping it did have.
 */
void
buf_acquire_nomap(struct buf *bp)
{
	splassert(IPL_BIO);
	SET(bp->b_flags, B_BUSY);
	if (bp->b_data != NULL) {
		TAILQ_REMOVE(&buf_valist, bp, b_valist);
		bcstats.kvaslots_avail--;
		bcstats.busymapped++;
	}
}

void
buf_map(struct buf *bp)
{
	vaddr_t va;

	splassert(IPL_BIO);

	if (bp->b_data == NULL) {
		unsigned long i;

		/*
		 * First, just use the pre-allocated space until we run out.
		 */
		if (buf_kva_start < buf_kva_end) {
			va = buf_kva_start;
			buf_kva_start += MAXPHYS;
			bcstats.kvaslots_avail--;
		} else {
			struct buf *vbp;

			/*
			 * Find some buffer we can steal the space from.
			 */
			vbp = TAILQ_FIRST(&buf_valist);
			while ((curproc != syncerproc &&
			   curproc != cleanerproc &&
			   bcstats.kvaslots_avail <= RESERVE_SLOTS) ||
			   vbp == NULL) {
				buf_needva++;
				tsleep_nsec(&buf_needva, PRIBIO, "buf_needva",
				    INFSLP);
				vbp = TAILQ_FIRST(&buf_valist);
			}
			va = buf_unmap(vbp);
		}

		for (i = 0; i < atop(bp->b_bufsize); i++) {
			struct vm_page *pg = uvm_pagelookup(bp->b_pobj,
			    bp->b_poffs + ptoa(i));

			KASSERT(pg != NULL);

			pmap_kenter_pa(va + ptoa(i), VM_PAGE_TO_PHYS(pg),
			    PROT_READ | PROT_WRITE);
		}
		pmap_update(pmap_kernel());
		bp->b_data = (caddr_t)va;
	} else {
		TAILQ_REMOVE(&buf_valist, bp, b_valist);
		bcstats.kvaslots_avail--;
	}

	bcstats.busymapped++;
}

void
buf_release(struct buf *bp)
{

	KASSERT(bp->b_flags & B_BUSY);
	splassert(IPL_BIO);

	if (bp->b_data) {
		bcstats.busymapped--;
		TAILQ_INSERT_TAIL(&buf_valist, bp, b_valist);
		bcstats.kvaslots_avail++;
		if (buf_needva) {
			buf_needva=0;
			wakeup(&buf_needva);
		}
	}
	CLR(bp->b_flags, B_BUSY);
}

/*
 * Deallocate all memory resources for this buffer. We need to be careful
 * to not drop kvm since we have no way to reclaim it. So, if the buffer
 * has kvm, we need to free it later. We put it on the front of the
 * freelist just so it gets picked up faster.
 *
 * Also, lots of assertions count on bp->b_data being NULL, so we
 * set it temporarily to NULL.
 *
 * Return non-zero if we take care of the freeing later.
 */
int
buf_dealloc_mem(struct buf *bp)
{
	caddr_t data;

	splassert(IPL_BIO);

	data = bp->b_data;
	bp->b_data = NULL;

	if (data) {
		if (bp->b_flags & B_BUSY)
			bcstats.busymapped--;
		pmap_kremove((vaddr_t)data, bp->b_bufsize);
		pmap_update(pmap_kernel());
	}

	if (bp->b_pobj)
		buf_free_pages(bp);

	if (data == NULL)
		return (0);

	bp->b_data = data;
	if (!(bp->b_flags & B_BUSY)) {		/* XXX - need better test */
		TAILQ_REMOVE(&buf_valist, bp, b_valist);
		bcstats.kvaslots_avail--;
	} else {
		CLR(bp->b_flags, B_BUSY);
		if (buf_needva) {
			buf_needva = 0;
			wakeup(&buf_needva);
		}
	}
	SET(bp->b_flags, B_RELEASED);
	TAILQ_INSERT_HEAD(&buf_valist, bp, b_valist);
	bcstats.kvaslots_avail++;

	return (1);
}

/*
 * Only used by bread_cluster.
 */
void
buf_fix_mapping(struct buf *bp, vsize_t newsize)
{
	vaddr_t va = (vaddr_t)bp->b_data;

	if (newsize < bp->b_bufsize) {
		pmap_kremove(va + newsize, bp->b_bufsize - newsize);
		pmap_update(pmap_kernel());
		/*
		 * Note: the size we lost is actually with the other
		 * buffers read in by bread_cluster
		 */
		bp->b_bufsize = newsize;
	}
}

vaddr_t
buf_unmap(struct buf *bp)
{
	vaddr_t va;

	KASSERT((bp->b_flags & B_BUSY) == 0);
	KASSERT(bp->b_data != NULL);
	splassert(IPL_BIO);

	TAILQ_REMOVE(&buf_valist, bp, b_valist);
	bcstats.kvaslots_avail--;
	va = (vaddr_t)bp->b_data;
	bp->b_data = NULL;
	pmap_kremove(va, bp->b_bufsize);
	pmap_update(pmap_kernel());

	if (bp->b_flags & B_RELEASED)
		pool_put(&bufpool, bp);

	return (va);
}

/* Always allocates in dma-reachable memory */
void
buf_alloc_pages(struct buf *bp, vsize_t size)
{
	int i;

	KASSERT(size == round_page(size));
	KASSERT(bp->b_pobj == NULL);
	KASSERT(bp->b_data == NULL);
	splassert(IPL_BIO);

	uvm_obj_init(&bp->b_uobj, &bufcache_pager, 1);

	/*
	 * Attempt to allocate with NOWAIT. if we can't, then throw
	 * away some clean pages and try again. Finally, if that
	 * fails, do a WAITOK allocation so the page daemon can find
	 * memory for us.
	 */
	do {
		i = uvm_pagealloc_multi(&bp->b_uobj, 0, size,
		    UVM_PLA_NOWAIT | UVM_PLA_NOWAKE);
		if (i == 0)
			break;
	} while	(bufbackoff(&dma_constraint, size) == 0);
	if (i != 0)
		i = uvm_pagealloc_multi(&bp->b_uobj, 0, size,
		    UVM_PLA_WAITOK);
	/* should not happen */
	if (i != 0)
		panic("uvm_pagealloc_multi unable to allocate an buf_object "
		    "of size %lu", size);

	bcstats.numbufpages += atop(size);
	bcstats.dmapages += atop(size);
	SET(bp->b_flags, B_DMA);
	bp->b_pobj = &bp->b_uobj;
	bp->b_poffs = 0;
	bp->b_bufsize = size;
}

void
buf_free_pages(struct buf *bp)
{
	struct uvm_object *uobj = bp->b_pobj;
	struct vm_page *pg;
	voff_t off, i;

	KASSERT(bp->b_data == NULL);
	KASSERT(uobj != NULL);
	splassert(IPL_BIO);

	off = bp->b_poffs;
	bp->b_pobj = NULL;
	bp->b_poffs = 0;

	for (i = 0; i < atop(bp->b_bufsize); i++) {
		pg = uvm_pagelookup(uobj, off + ptoa(i));
		KASSERT(pg != NULL);
		KASSERT(pg->wire_count == 1);
		pg->wire_count = 0;
		bcstats.numbufpages--;
		if (ISSET(bp->b_flags, B_DMA))
			bcstats.dmapages--;
	}
	CLR(bp->b_flags, B_DMA);

	/* XXX refactor to do this without splbio later */
	uvm_obj_free(uobj);
}

/* Reallocate a buf into a particular pmem range specified by "where". */
int
buf_realloc_pages(struct buf *bp, struct uvm_constraint_range *where,
    int flags)
{
	vaddr_t va;
	int dma;
  	int i, r;
	KASSERT(!(flags & UVM_PLA_WAITOK) ^ !(flags & UVM_PLA_NOWAIT));

	splassert(IPL_BIO);
	KASSERT(ISSET(bp->b_flags, B_BUSY));
	dma = ISSET(bp->b_flags, B_DMA);

	/* if the original buf is mapped, unmap it */
	if (bp->b_data != NULL) {
		va = (vaddr_t)bp->b_data;
		pmap_kremove(va, bp->b_bufsize);
		pmap_update(pmap_kernel());
	}

	do {
		r = uvm_pagerealloc_multi(bp->b_pobj, bp->b_poffs,
		    bp->b_bufsize, UVM_PLA_NOWAIT | UVM_PLA_NOWAKE, where);
		if (r == 0)
			break;
	} while	((bufbackoff(where, atop(bp->b_bufsize)) == 0));

	/*
	 * bufbackoff() failed, so there's no more we can do without
	 * waiting.  If allowed do, make that attempt.
	 */
	if (r != 0 && (flags & UVM_PLA_WAITOK))
		r = uvm_pagerealloc_multi(bp->b_pobj, bp->b_poffs,
		    bp->b_bufsize, flags, where);

	/*
	 * If the allocation has succeeded, we may be somewhere different.
	 * If the allocation has failed, we are in the same place.
	 *
	 * We still have to re-map the buffer before returning.
	 */

	/* take it out of dma stats until we know where we are */
	if (dma)
		bcstats.dmapages -= atop(bp->b_bufsize);

	dma = 1;
	/* if the original buf was mapped, re-map it */
	for (i = 0; i < atop(bp->b_bufsize); i++) {
		struct vm_page *pg = uvm_pagelookup(bp->b_pobj,
		    bp->b_poffs + ptoa(i));
		KASSERT(pg != NULL);
		if  (!PADDR_IS_DMA_REACHABLE(VM_PAGE_TO_PHYS(pg)))
			dma = 0;
		if (bp->b_data != NULL) {
			pmap_kenter_pa(va + ptoa(i), VM_PAGE_TO_PHYS(pg),
			    PROT_READ|PROT_WRITE);
			pmap_update(pmap_kernel());
		}
	}
	if (dma) {
		SET(bp->b_flags, B_DMA);
		bcstats.dmapages += atop(bp->b_bufsize);
	} else
		CLR(bp->b_flags, B_DMA);
	return(r);
}