> -----Original Message-----
> From: Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>
> Sent: Monday, June 22, 2020 7:02 AM
> To: Williams, Dan J <dan.j.williams@xxxxxxxxx>; Kaneda, Erik
> <erik.kaneda@xxxxxxxxx>
> Cc: Wysocki, Rafael J <rafael.j.wysocki@xxxxxxxxx>; Len Brown
> <lenb@xxxxxxxxxx>; Borislav Petkov <bp@xxxxxxxxx>; Weiny, Ira
> <ira.weiny@xxxxxxxxx>; James Morse <james.morse@xxxxxxx>; Myron
> Stowe <myron.stowe@xxxxxxxxxx>; Andy Shevchenko
> <andriy.shevchenko@xxxxxxxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; linux-
> acpi@xxxxxxxxxxxxxxx; linux-nvdimm@xxxxxxxxxxxx; Moore, Robert
> <robert.moore@xxxxxxxxx>
> Subject: [RFT][PATCH v2 3/4] ACPICA: Preserve memory opregion mappings
> if supported by OS
>
> From: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx>
>
> The ACPICA's strategy with respect to the handling of memory mappings
> associated with memory operation regions is to avoid mapping the
> entire region at once which may be problematic at least in principle
> (for example, it may lead to conflicts with overlapping mappings
> having different attributes created by drivers). It may also be
> wasteful, because memory opregions on some systems take up vast
> chunks of address space while the fields in those regions actually
> accessed by AML are sparsely distributed.
>
> For this reason, a one-page "window" is mapped for a given opregion
> on the first memory access through it and if that "window" does not
> cover an address range accessed through that opregion subsequently,
> it is unmapped and a new "window" is mapped to replace it. Next,
> if the new "window" is not sufficient to access memory through the
> opregion in question in the future, it will be replaced with yet
> another "window" and so on. That may lead to a suboptimal sequence
> of memory mapping and unmapping operations, for example if two fields
> in one opregion separated from each other by a sufficiently wide
> chunk of unused address space are accessed in an alternating pattern.
>
> The situation may still be suboptimal if the deferred unmapping
> introduced previously is supported by the OS layer. For instance,
> the alternating memory access pattern mentioned above may produce
> a relatively long list of mappings to release with substantial
> duplication among the entries in it, which could be avoided if
> acpi_ex_system_memory_space_handler() did not release the mapping
> used by it previously as soon as the current access was not covered
> by it.
>
> In order to improve that, modify acpi_ex_system_memory_space_handler()
> to take advantage of the memory mappings reference counting at the OS
> level if a suitable interface is provided.
>
Hi,
> Namely, if ACPI_USE_FAST_PATH_MAPPING is set, the OS is expected to
> implement acpi_os_map_memory_fast_path() that will return NULL if
> there is no mapping covering the given address range known to it.
> If such a mapping is there, however, its reference counter will be
> incremented and a pointer representing the requested virtual address
> will be returned right away without any additional consequences.
I do not fully understand why this is under a #ifdef. Is this to support operating systems that might not want to add support for this behavior?
Also, instead of using the terminology fast_path, I think it would be easier to use terminology that describes the mechanism..
It might be easier for other Operating systems to understand something like acpi_os_map_preserved_memory or acpi_os_map_sysmem_opregion_memory.
Thanks,
Erik
>
> That allows acpi_ex_system_memory_space_handler() to acquire
> additional references to all new memory mappings with the help
> of acpi_os_map_memory_fast_path() so as to retain them until the
> memory opregions associated with them go away. The function will
> still use a new "window" mapping if the current one does not
> cover the address range at hand, but it will avoid unmapping the
> current one right away by adding it to a list of "known" mappings
> associated with the given memory opregion which will be deleted at
> the opregion deactivation time. The mappings in that list can be
> used every time a "new window" is needed so as to avoid overhead
> related to the mapping and unmapping of memory.
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> ---
> drivers/acpi/acpica/acinterp.h | 4 +
> drivers/acpi/acpica/evrgnini.c | 7 +-
> drivers/acpi/acpica/exregion.c | 159
> ++++++++++++++++++++++++++++++++-
> 3 files changed, 162 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/acpi/acpica/acinterp.h b/drivers/acpi/acpica/acinterp.h
> index 1f1026fb06e9..db9c279baa2e 100644
> --- a/drivers/acpi/acpica/acinterp.h
> +++ b/drivers/acpi/acpica/acinterp.h
> @@ -479,8 +479,12 @@ void acpi_ex_pci_cls_to_string(char *dest, u8
> class_code[3]);
>
> u8 acpi_is_valid_space_id(u8 space_id);
>
> +struct acpi_mem_space_context
> *acpi_ex_alloc_mem_space_context(void);
> +
> void acpi_ex_unmap_region_memory(struct acpi_mem_space_context
> *mem_info);
>
> +void acpi_ex_unmap_all_region_mappings(struct
> acpi_mem_space_context *mem_info);
> +
> /*
> * exregion - default op_region handlers
> */
> diff --git a/drivers/acpi/acpica/evrgnini.c b/drivers/acpi/acpica/evrgnini.c
> index 9f33114a74ca..f6c5feea10bc 100644
> --- a/drivers/acpi/acpica/evrgnini.c
> +++ b/drivers/acpi/acpica/evrgnini.c
> @@ -46,10 +46,10 @@ acpi_ev_system_memory_region_setup(acpi_handle
> handle,
> local_region_context =
> (struct acpi_mem_space_context
> *)*region_context;
>
> - /* Delete a cached mapping if present */
> + /* Delete memory mappings if present */
>
> if (local_region_context->mapped_length) {
> -
> acpi_ex_unmap_region_memory(local_region_context);
> +
> acpi_ex_unmap_all_region_mappings(local_region_context);
> }
> ACPI_FREE(local_region_context);
> *region_context = NULL;
> @@ -59,8 +59,7 @@ acpi_ev_system_memory_region_setup(acpi_handle
> handle,
>
> /* Create a new context */
>
> - local_region_context =
> - ACPI_ALLOCATE_ZEROED(sizeof(struct
> acpi_mem_space_context));
> + local_region_context = acpi_ex_alloc_mem_space_context();
> if (!(local_region_context)) {
> return_ACPI_STATUS(AE_NO_MEMORY);
> }
> diff --git a/drivers/acpi/acpica/exregion.c b/drivers/acpi/acpica/exregion.c
> index af777b7fccb0..9d97b6a67074 100644
> --- a/drivers/acpi/acpica/exregion.c
> +++ b/drivers/acpi/acpica/exregion.c
> @@ -14,6 +14,40 @@
> #define _COMPONENT ACPI_EXECUTER
> ACPI_MODULE_NAME("exregion")
>
> +struct acpi_mem_mapping {
> + acpi_physical_address physical_address;
> + u8 *logical_address;
> + acpi_size length;
> + struct acpi_mem_mapping *next_mm;
> +};
> +
> +struct acpi_mm_context {
> + struct acpi_mem_space_context mem_info;
> + struct acpi_mem_mapping *first_mm;
> +};
> +
> +/*********************************************************
> ********************
> + *
> + * FUNCTION: acpi_ex_alloc_mem_space_context
> + *
> + * PARAMETERS: None
> + *
> + * RETURN: Pointer to a new region context object.
> + *
> + * DESCRIPTION: Allocate memory for memory operation region
> representation.
> + *
> +
> **********************************************************
> ******************/
> +struct acpi_mem_space_context
> *acpi_ex_alloc_mem_space_context(void)
> +{
> + ACPI_FUNCTION_TRACE(acpi_ex_alloc_mem_space_context);
> +
> +#ifdef ACPI_USE_FAST_PATH_MAPPING
> + return ACPI_ALLOCATE_ZEROED(sizeof(struct acpi_mm_context));
> +#else
> + return ACPI_ALLOCATE_ZEROED(sizeof(struct
> acpi_mem_space_context));
> +#endif
> +}
> +
>
> /**********************************************************
> *******************
> *
> * FUNCTION: acpi_ex_unmap_region_memory
> @@ -40,6 +74,44 @@ void acpi_ex_unmap_region_memory(struct
> acpi_mem_space_context *mem_info)
> return_VOID;
> }
>
> +/*********************************************************
> ********************
> + *
> + * FUNCTION: acpi_ex_unmap_all_region_mappings
> + *
> + * PARAMETERS: mem_info - Region specific context
> + *
> + * RETURN: None
> + *
> + * DESCRIPTION: Unmap all mappings associated with a memory operation
> region.
> + *
> +
> **********************************************************
> ******************/
> +void acpi_ex_unmap_all_region_mappings(struct
> acpi_mem_space_context *mem_info)
> +{
> +#ifdef ACPI_USE_FAST_PATH_MAPPING
> + struct acpi_mm_context *mm_context = (struct acpi_mm_context
> *)mem_info;
> + struct acpi_mem_mapping *mm;
> +#endif
> +
> + ACPI_FUNCTION_TRACE(acpi_ex_unmap_all_region_mappings);
> +
> + acpi_ex_unmap_region_memory(mem_info);
> +
> +#ifdef ACPI_USE_FAST_PATH_MAPPING
> + while (mm_context->first_mm) {
> + mm = mm_context->first_mm;
> + mm_context->first_mm = mm->next_mm;
> +#ifdef ACPI_USE_DEFERRED_UNMAPPING
> + acpi_os_unmap_deferred(mm->logical_address, mm-
> >length);
> +#else
> + acpi_os_unmap_memory(mm->logical_address, mm-
> >length);
> +#endif
> + ACPI_FREE(mm);
> + }
> +#endif /* ACPI_USE_FAST_PATH_MAPPING */
> +
> + return_VOID;
> +}
> +
>
> /**********************************************************
> *********************
> *
> * FUNCTION: acpi_ex_system_memory_space_handler
> @@ -70,6 +142,10 @@ acpi_ex_system_memory_space_handler(u32
> function,
> u32 length;
> acpi_size map_length;
> acpi_size page_boundary_map_length;
> +#ifdef ACPI_USE_FAST_PATH_MAPPING
> + struct acpi_mm_context *mm_context = (struct acpi_mm_context
> *)mem_info;
> + struct acpi_mem_mapping *mm;
> +#endif
> #ifdef ACPI_MISALIGNMENT_NOT_SUPPORTED
> u32 remainder;
> #endif
> @@ -128,7 +204,7 @@ acpi_ex_system_memory_space_handler(u32
> function,
> mem_info->mapped_length))) {
> /*
> * The request cannot be resolved by the current memory
> mapping;
> - * Delete the existing mapping and create a new one.
> + * Delete the current cached mapping and get a new one.
> */
> if (mem_info->mapped_length) {
>
> @@ -137,6 +213,36 @@ acpi_ex_system_memory_space_handler(u32
> function,
> acpi_ex_unmap_region_memory(mem_info);
> }
>
> +#ifdef ACPI_USE_FAST_PATH_MAPPING
> + /*
> + * Look for an existing saved mapping matching the address
> range
> + * at hand. If found, make the OS layer bump up the
> reference
> + * counter of that mapping, cache it and carry out the access.
> + */
> + for (mm = mm_context->first_mm; mm; mm = mm-
> >next_mm) {
> + if (address < mm->physical_address)
> + continue;
> +
> + if ((u64)address + length >
> + (u64)mm->physical_address + mm-
> >length)
> + continue;
> +
> + /*
> + * When called on a known-existing memory mapping,
> + * acpi_os_map_memory_fast_path() must return
> the same
> + * logical address as before or NULL.
> + */
> + if (!acpi_os_map_memory_fast_path(mm-
> >physical_address,
> + mm->length))
> + continue;
> +
> + mem_info->mapped_logical_address = mm-
> >logical_address;
> + mem_info->mapped_physical_address = mm-
> >physical_address;
> + mem_info->mapped_length = mm->length;
> + goto access;
> + }
> +#endif /* ACPI_USE_FAST_PATH_MAPPING */
> +
> /*
> * October 2009: Attempt to map from the requested
> address to the
> * end of the region. However, we will never map more than
> one
> @@ -168,9 +274,8 @@ acpi_ex_system_memory_space_handler(u32
> function,
>
> /* Create a new mapping starting at the address given */
>
> - mem_info->mapped_logical_address =
> - acpi_os_map_memory(address, map_length);
> - if (!mem_info->mapped_logical_address) {
> + logical_addr_ptr = acpi_os_map_memory(address,
> map_length);
> + if (!logical_addr_ptr) {
> ACPI_ERROR((AE_INFO,
> "Could not map memory at 0x%8.8X%8.8X,
> size %u",
> ACPI_FORMAT_UINT64(address),
> @@ -181,10 +286,56 @@ acpi_ex_system_memory_space_handler(u32
> function,
>
> /* Save the physical address and mapping size */
>
> + mem_info->mapped_logical_address = logical_addr_ptr;
> mem_info->mapped_physical_address = address;
> mem_info->mapped_length = map_length;
> +
> +#ifdef ACPI_USE_FAST_PATH_MAPPING
> + /*
> + * Create a new mm list entry to save the new mapping for
> + * removal at the operation region deactivation time.
> + */
> + mm = ACPI_ALLOCATE_ZEROED(sizeof(*mm));
> + if (!mm) {
> + /*
> + * No room to save the new mapping, but this is not
> + * critical. Just log the error and carry out the
> + * access as requested.
> + */
> + ACPI_ERROR((AE_INFO,
> + "Not enough memory to save memory
> mapping at 0x%8.8X%8.8X, size %u",
> + ACPI_FORMAT_UINT64(address),
> + (u32)map_length));
> + goto access;
> + }
> + /*
> + * Bump up the new mapping's reference counter in the OS
> layer
> + * to prevent it from getting dropped prematurely.
> + */
> + if (!acpi_os_map_memory_fast_path(address, map_length))
> {
> + /*
> + * Something has gone wrong, but this is not critical.
> + * Log the error, free the mm list entry that won't be
> + * used and carry out the access as requested.
> + */
> + ACPI_ERROR((AE_INFO,
> + "Unable to save memory mapping at
> 0x%8.8X%8.8X, size %u",
> + ACPI_FORMAT_UINT64(address),
> + (u32)map_length));
> + ACPI_FREE(mm);
> + goto access;
> + }
> + mm->physical_address = address;
> + mm->logical_address = logical_addr_ptr;
> + mm->length = map_length;
> + mm->next_mm = mm_context->first_mm;
> + mm_context->first_mm = mm;
> }
>
> +access:
> +#else /* !ACPI_USE_FAST_PATH_MAPPING */
> + }
> +#endif /* !ACPI_USE_FAST_PATH_MAPPING */
> /*
> * Generate a logical pointer corresponding to the address we want
> to
> * access
> --
> 2.26.2
>
>
>
