Re: [PATCH] firmware: qcom_scm: Introduce batching of hyp assign calls

[Konrad Dybcio]

On 9.02.2024 19:06, Elliot Berman wrote:
> On Fri, Feb 09, 2024 at 04:55:36PM +0530, Dibakar Singh wrote:
>> Expose an API qcom_scm_assign_table to allow client drivers to batch
>> multiple memory regions in a single hyp assign call.
>>
>> In the existing situation, if our goal is to process an sg_table and
>> transfer its ownership from the current VM to a different VM, we have a
>> couple of strategies. The first strategy involves processing the entire
>> sg_table at once and then transferring the ownership. However, this
>> method may have an adverse impact on the system because during an SMC
>> call, the NS interrupts are disabled, and this delay could be
>> significant when dealing with large sg_tables. To address this issue, we
>> can adopt a second strategy, which involves processing each sg_list in
>> the sg_table individually and reassigning memory ownership. Although
>> this method is slower and potentially impacts performance, it will not
>> keep the NS interrupts disabled for an extended period.
>>
>> A more efficient strategy is to process the sg_table in batches. This
>> approach addresses both scenarios by involving memory processing in
>> batches, thus avoiding prolonged NS interrupt disablement for longer
>> duration when dealing with large sg_tables. Moreover, since we process
>> in batches, this method is faster compared to processing each item
>> individually. The observations on testing both the approaches for
>> performance is as follows:
>>
>> Allocation Size/            256MB            512MB            1024MB
>> Algorithm Used           ===========      ===========      ============
>>
>> Processing each sg_list   73708(us)        149289(us)       266964(us)
>> in sg_table one by one
>>
>> Processing sg_table in    46925(us)         92691(us)       176893(us)
>> batches
>>
>> This implementation serves as a wrapper around the helper function
>> __qcom_scm_assign_mem, which takes an sg_list and processes it in
>> batches. We’ve set the limit to a minimum of 32 sg_list in a batch or a
>> total batch size of 512 pages. The selection of these numbers is
>> heuristic, based on the test runs conducted. Opting for a smaller number
>> would compromise performance, while a larger number would result in
>> non-secure interrupts being disabled for an extended duration.
>>
>> Co-developed-by: Prakruthi Deepak Heragu <quic_pheragu@xxxxxxxxxxx>
>> Signed-off-by: Prakruthi Deepak Heragu <quic_pheragu@xxxxxxxxxxx>
>> Signed-off-by: Dibakar Singh <quic_dibasing@xxxxxxxxxxx>
>> ---
>>  drivers/firmware/qcom/qcom_scm.c       | 211 +++++++++++++++++++++++++
>>  include/linux/firmware/qcom/qcom_scm.h |   7 +
>>  2 files changed, 218 insertions(+)
>>
>> diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
>> index 520de9b5633a..038b96503d65 100644
>> --- a/drivers/firmware/qcom/qcom_scm.c
>> +++ b/drivers/firmware/qcom/qcom_scm.c
>> @@ -21,6 +21,8 @@
>>  #include <linux/platform_device.h>
>>  #include <linux/reset-controller.h>
>>  #include <linux/types.h>
>> +#include <linux/scatterlist.h>
>> +#include <linux/slab.h>
>>  
>>  #include "qcom_scm.h"
>>  
>> @@ -1048,6 +1050,215 @@ int qcom_scm_assign_mem(phys_addr_t mem_addr, size_t mem_sz,
>>  }
>>  EXPORT_SYMBOL_GPL(qcom_scm_assign_mem);
>>  
>> +/**
>> + * qcom_scm_assign_mem_batch() - Make a secure call to reassign memory
>> + *				   ownership of several memory regions
>> + * @mem_regions:    A buffer describing the set of memory regions that need to
>> + *		    be reassigned
>> + * @nr_mem_regions: The number of memory regions that need to be reassigned
>> + * @srcvms:	    A buffer populated with he vmid(s) for the current set of
>> + *		    owners
>> + * @src_sz:	    The size of the srcvms buffer (in bytes)
>> + * @destvms:	    A buffer populated with the new owners and corresponding
>> + *		    permission flags.
>> + * @dest_sz:	    The size of the destvms buffer (in bytes)
>> + *
>> + * Return negative errno on failure, 0 on success.
>> + */
>> +static int qcom_scm_assign_mem_batch(struct qcom_scm_mem_map_info *mem_regions,
>> +				     size_t nr_mem_regions, u32 *srcvms,
>> +				     size_t src_sz,
>> +				     struct qcom_scm_current_perm_info *destvms,
>> +				     size_t dest_sz)
>> +{
>> +	dma_addr_t mem_dma_addr;
>> +	size_t mem_regions_sz;
>> +	int ret = 0, i;
>> +
>> +	for (i = 0; i < nr_mem_regions; i++) {
>> +		mem_regions[i].mem_addr = cpu_to_le64(mem_regions[i].mem_addr);
>> +		mem_regions[i].mem_size = cpu_to_le64(mem_regions[i].mem_size);
>> +	}
>> +
>> +	mem_regions_sz = nr_mem_regions * sizeof(*mem_regions);
>> +	mem_dma_addr = dma_map_single(__scm->dev, mem_regions, mem_regions_sz,
>> +				      DMA_TO_DEVICE);
>> +	if (dma_mapping_error(__scm->dev, mem_dma_addr)) {
>> +		dev_err(__scm->dev, "mem_dma_addr mapping failed\n");
>> +		return -ENOMEM;
>> +	}
>> +
>> +	ret = __qcom_scm_assign_mem(__scm->dev, virt_to_phys(mem_regions),
>> +				    mem_regions_sz, virt_to_phys(srcvms), src_sz,
>> +				    virt_to_phys(destvms), dest_sz);
>> +
>> +	dma_unmap_single(__scm->dev, mem_dma_addr, mem_regions_sz, DMA_TO_DEVICE);
>> +	return ret;
>> +}
>> +
>> +/**
>> + * qcom_scm_prepare_mem_batch() - Prepare batches of memory regions
>> + * @sg_table:       A scatter list whose memory needs to be reassigned
>> + * @srcvms:	    A buffer populated with he vmid(s) for the current set of
>> + *		    owners
>> + * @nr_src:	    The number of the src_vms buffer
>> + * @destvms:	    A buffer populated with he vmid(s) for the new owners
>> + * @destvms_perms:  A buffer populated with the permission flags of new owners
>> + * @nr_dest:	    The number of the destvms
>> + * @last_sgl:	    Denotes to the last scatter list element. Used in case of rollback
>> + * @roll_back:	    Identifies whether we are executing rollback in case of failure
>> + *
>> + * Return negative errno on failure, 0 on success.
>> + */
>> +static int qcom_scm_prepare_mem_batch(struct sg_table *table,
>> +				      u32 *srcvms, int nr_src,
>> +				      int *destvms, int *destvms_perms,
>> +				      int nr_dest,
>> +				      struct scatterlist *last_sgl, bool roll_back)
>> +{
>> +	struct qcom_scm_current_perm_info *destvms_cp;
>> +	struct qcom_scm_mem_map_info *mem_regions_buf;
>> +	struct scatterlist *curr_sgl = table->sgl;
>> +	dma_addr_t source_dma_addr, dest_dma_addr;
>> +	size_t batch_iterator;
>> +	size_t batch_start = 0;
>> +	size_t destvms_cp_sz;
>> +	size_t srcvms_cp_sz;
>> +	size_t batch_size;
>> +	u32 *srcvms_cp;
>> +	int ret = 0;
>> +	int i;
>> +
>> +	if (!table || !table->sgl || !srcvms || !nr_src ||
>> +	    !destvms || !destvms_perms || !nr_dest || !table->nents)
>> +		return -EINVAL;
>> +
>> +	srcvms_cp_sz = sizeof(*srcvms_cp) * nr_src;
>> +	srcvms_cp = kmemdup(srcvms, srcvms_cp_sz, GFP_KERNEL);
>> +	if (!srcvms_cp)
>> +		return -ENOMEM;
>> +
>> +	for (i = 0; i < nr_src; i++)
>> +		srcvms_cp[i] = cpu_to_le32(srcvms_cp[i]);
>> +
>> +	source_dma_addr = dma_map_single(__scm->dev, srcvms_cp,
>> +					 srcvms_cp_sz, DMA_TO_DEVICE);
> 
> Please use the new tzmem allocator:
> 
> https://lore.kernel.org/all/20240205182810.58382-1-brgl@xxxxxxxx/

And the new __free annotations, please

Konrad