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

[Dibakar Singh <quic_dibasing@quicinc.com>]

On 12-Feb-24 4:39 PM, Konrad Dybcio wrote:
> 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@quicinc.com>
>>> Signed-off-by: Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>
>>> Signed-off-by: Dibakar Singh <quic_dibasing@quicinc.com>
>>> ---
>>>   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@bgdev.pl/
> 
> And the new __free annotations, please
> 

Noted, I will incorporate these changes in the V2 patch.

> Konrad

Thanks,
Dibakar