On 02/10/24(Wed) 17:28, Martin Pieuchot wrote:
> It is currently impossible to use km_alloc(9) to get a managed mapping
> backed with physical pages allocated up front.  I guess this is why
> uvm_km_kmemalloc_pla() is still used to allocate the UAREA.
> 
> To fix that, I suggest the diff below which turns the "kp_pageable" flag
> of km_alloc(9) into a "kp_managed".  This new flag no longer implies
> "kp_nomem" so I updated the description and fixed the remaining XXX to
> preserve existing behavior of the `kp_pageable' global.
> 
> With this change I believe we could also get rid of uvm_km_zalloc() used
> in the i386 pmap.
> 
> Comments?  Oks?

Anyone?

> Index: sys/uvm/uvm_extern.h
> ===================================================================
> RCS file: /cvs/src/sys/uvm/uvm_extern.h,v
> diff -u -p -r1.177 uvm_extern.h
> --- sys/uvm/uvm_extern.h	24 Aug 2024 10:46:43 -0000	1.177
> +++ sys/uvm/uvm_extern.h	2 Oct 2024 14:51:32 -0000
> @@ -328,7 +328,7 @@ struct kmem_va_mode {
>   *  kp_nomem - don't allocate any backing pages.
>   *  kp_maxseg - maximal amount of contiguous segments.
>   *  kp_zero - zero the returned memory.
> - *  kp_pageable - allocate pageable memory.
> + *  kp_managed - map memory paged from `kp_object'.
>   */
>  struct kmem_pa_mode {
>  	struct uvm_constraint_range *kp_constraint;
> @@ -338,7 +338,7 @@ struct kmem_pa_mode {
>  	int kp_maxseg;
>  	char kp_nomem;
>  	char kp_zero;
> -	char kp_pageable;
> +	char kp_managed;
>  };
>  
>  /*
> Index: sys/uvm/uvm_glue.c
> ===================================================================
> RCS file: /cvs/src/sys/uvm/uvm_glue.c,v
> diff -u -p -r1.84 uvm_glue.c
> --- sys/uvm/uvm_glue.c	10 Sep 2022 20:35:29 -0000	1.84
> +++ sys/uvm/uvm_glue.c	2 Oct 2024 14:39:14 -0000
> @@ -259,20 +259,26 @@ uvm_vsunlock_device(struct proc *p, void
>  	uvm_km_free(kernel_map, kva, sz);
>  }
>  
> +const struct kmem_va_mode kv_uarea = {
> +	.kv_map = &kernel_map,
> +	.kv_align = USPACE_ALIGN
> +};
> +
> +const struct kmem_pa_mode kp_uarea = {
> +	.kp_constraint = &no_constraint,
> +	.kp_object = &uvm.kernel_object,
> +	.kp_zero = 1,
> +	.kp_managed = 1
> +};
> +
>  /*
>   * uvm_uarea_alloc: allocate the u-area for a new thread
>   */
>  vaddr_t
>  uvm_uarea_alloc(void)
>  {
> -	vaddr_t uaddr;
> -
> -	uaddr = uvm_km_kmemalloc_pla(kernel_map, uvm.kernel_object, USPACE,
> -	    USPACE_ALIGN, UVM_KMF_ZERO,
> -	    no_constraint.ucr_low, no_constraint.ucr_high,
> -	    0, 0, USPACE/PAGE_SIZE);
>  
> -	return (uaddr);
> +	return (vaddr_t)km_alloc(USPACE, &kv_uarea, &kp_uarea, &kd_waitok);
>  }
>  
>  /*
> @@ -284,7 +290,7 @@ uvm_uarea_alloc(void)
>  void
>  uvm_uarea_free(struct proc *p)
>  {
> -	uvm_km_free(kernel_map, (vaddr_t)p->p_addr, USPACE);
> +	km_free(p->p_addr, USPACE, &kv_uarea, &kp_uarea);
>  	p->p_addr = NULL;
>  }
>  
> Index: sys/uvm/uvm_km.c
> ===================================================================
> RCS file: /cvs/src/sys/uvm/uvm_km.c,v
> diff -u -p -r1.154 uvm_km.c
> --- sys/uvm/uvm_km.c	24 Aug 2024 10:46:43 -0000	1.154
> +++ sys/uvm/uvm_km.c	2 Oct 2024 14:49:00 -0000
> @@ -743,7 +743,7 @@ km_alloc(size_t sz, const struct kmem_va
>  
>  	TAILQ_INIT(&pgl);
>  
> -	if (kp->kp_nomem || kp->kp_pageable)
> +	if (kp->kp_nomem)
>  		goto alloc_va;
>  
>  	pla_flags = kd->kd_waitok ? UVM_PLA_WAITOK : UVM_PLA_NOWAIT;
> @@ -753,7 +753,8 @@ km_alloc(size_t sz, const struct kmem_va
>  
>  	pla_align = kp->kp_align;
>  #ifdef __HAVE_PMAP_DIRECT
> -	if (pla_align < kv->kv_align)
> +	if ((kv->kv_singlepage || kp->kp_maxseg == 1) &&
> +	    (pla_align < kv->kv_align))
>  		pla_align = kv->kv_align;
>  #endif
>  	pla_maxseg = kp->kp_maxseg;
> @@ -762,7 +763,7 @@ km_alloc(size_t sz, const struct kmem_va
>  
>  	if (uvm_pglistalloc(sz, kp->kp_constraint->ucr_low,
>  	    kp->kp_constraint->ucr_high, pla_align, kp->kp_boundary,
> -	    &pgl, pla_maxseg, pla_flags)) {	
> +	    &pgl, pla_maxseg, pla_flags)) {
>  		return (NULL);
>  	}
>  
> @@ -783,7 +784,7 @@ km_alloc(size_t sz, const struct kmem_va
>  alloc_va:
>  	prot = PROT_READ | PROT_WRITE;
>  
> -	if (kp->kp_pageable) {
> +	if (kp->kp_managed) {
>  		KASSERT(kp->kp_object);
>  		KASSERT(!kv->kv_singlepage);
>  	} else {
> @@ -838,7 +839,7 @@ try_map:
>  	}
>  	sva = va;
>  	TAILQ_FOREACH(pg, &pgl, pageq) {
> -		if (kp->kp_pageable)
> +		if (kp->kp_managed)
>  			pmap_enter(pmap_kernel(), va, VM_PAGE_TO_PHYS(pg),
>  			    prot, prot | PMAP_WIRED);
>  		else
> @@ -860,9 +861,6 @@ km_free(void *v, size_t sz, const struct
>  	sva = (vaddr_t)v;
>  	eva = sva + sz;
>  
> -	if (kp->kp_nomem)
> -		goto free_va;
> -
>  #ifdef __HAVE_PMAP_DIRECT
>  	if (kv->kv_singlepage || kp->kp_maxseg == 1) {
>  		TAILQ_INIT(&pgl);
> @@ -887,10 +885,10 @@ km_free(void *v, size_t sz, const struct
>  	}
>  #endif
>  
> -	if (kp->kp_pageable) {
> +	if (kp->kp_managed) {
>  		pmap_remove(pmap_kernel(), sva, eva);
>  		pmap_update(pmap_kernel());
> -	} else {
> +	} else if (!kp->kp_nomem) {
>  		TAILQ_INIT(&pgl);
>  		for (va = sva; va < eva; va += PAGE_SIZE) {
>  			paddr_t pa;
> @@ -908,7 +906,7 @@ km_free(void *v, size_t sz, const struct
>  		pmap_update(pmap_kernel());
>  		uvm_pglistfree(&pgl);
>  	}
> -free_va:
> +
>  	uvm_unmap(*kv->kv_map, sva, eva);
>  	if (kv->kv_wait)
>  		wakeup(*kv->kv_map);
> @@ -951,8 +949,8 @@ const struct kmem_pa_mode kp_zero = {
>  
>  const struct kmem_pa_mode kp_pageable = {
>  	.kp_object = &uvm.kernel_object,
> -	.kp_pageable = 1
> -/* XXX - kp_nomem, maybe, but we'll need to fix km_free. */
> +	.kp_managed = 1,
> +	.kp_nomem = 1
>  };
>  
>  const struct kmem_pa_mode kp_none = {
> Index: share/man/man9/km_alloc.9
> ===================================================================
> RCS file: /cvs/src/share/man/man9/km_alloc.9,v
> diff -u -p -r1.9 km_alloc.9
> --- share/man/man9/km_alloc.9	6 Dec 2019 19:15:16 -0000	1.9
> +++ share/man/man9/km_alloc.9	2 Oct 2024 14:47:18 -0000
> @@ -126,7 +126,7 @@ struct kmem_pa_mode {
>  	int kp_nomem;
>  	int kp_maxseg;
>  	int kp_zero;
> -	int kp_pageable;
> +	int kp_managed;
>  };
>  .Ed
>  .Bl -tag -width kp_constraint
> @@ -141,15 +141,14 @@ Physical alignment of the first page in 
>  Boundary that the physical addresses can't cross if the allocation is
>  contiguous.
>  .It kp_nomem
> -A flag that specifies that the allocation should not be backed by physical
> -pages.
> +A flag that specifies that no physical page should be allocated up front.
>  .It kp_maxseg
>  Maximal amount of contiguous physical segments in the allocation.
>  .It kp_zero
>  A flag that specifies if the returned memory should be zeroed.
> -.It kp_pageable
> -A flag that specifies if the returned memory should be demand paged from the
> -backing object instead of being allocated up front.
> +.It kp_managed
> +A flag that specifies if the returned memory should be mapped paged from the
> +backing object.
>  .El
>  .Bd -literal
>  struct kmem_dyn_mode {
>