Thanks for looking into this patch David,
David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> writes:
> On Thu, Apr 15, 2021 at 01:23:43PM +0530, Vaibhav Jain wrote:
>> Add support for H_SCM_PERFORMANCE_STATS described at [1] for
>> spapr nvdimms. This enables guest to fetch performance stats[2] like
>> expected life of an nvdimm ('MemLife ') etc and display them to the
>> user. Linux kernel support for fetching these performance stats and
>> exposing them to the user-space was done via [3].
>>
>> The hcall semantics mandate that each nvdimm performance stats is
>> uniquely identied by a 8-byte ascii string (e.g 'MemLife ') and its
>> value be a 8-byte integer. These performance-stats are exchanged with
>> the guest in via a guest allocated buffer called
>> 'requestAndResultBuffer' or rr-buffer for short. This buffer contains
>> a header descibed by 'struct papr_scm_perf_stats' followed by an array
>> of performance-stats described by 'struct papr_scm_perf_stat'. The
>> hypervisor is expected to validate the rr-buffer header and then based
>> on the request copy the needed performance-stats to the array of
>> 'struct papr_scm_perf_stat' following the header.
>>
>> The patch proposes a new function h_scm_performance_stats() that
>> services the H_SCM_PERFORMANCE_STATS hcall. After verifying the
>> validity of the rr-buffer header via scm_perf_check_rr_buffer() it
>> proceeds to fill the rr-buffer with requested performance-stats. The
>> value of individual stats is retrived from individual accessor
>> function for the stat which are indexed in the array
>> 'nvdimm_perf_stats'.
>>
>> References:
>> [1] "Hypercall Op-codes (hcalls)"
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/powerpc/papr_hcalls.rst#n269
>> [2] Sysfs attribute documentation for papr_scm
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/ABI/testing/sysfs-bus-papr-pmem#n36
>> [3] "powerpc/papr_scm: Fetch nvdimm performance stats from PHYP"
>> https://lore.kernel.org/r/20200731064153.182203-2-vaibhav@xxxxxxxxxxxxx
>>
>> Signed-off-by: Vaibhav Jain <vaibhav@xxxxxxxxxxxxx>
>> ---
>> hw/ppc/spapr_nvdimm.c | 243 +++++++++++++++++++++++++++++++++++++++++
>> include/hw/ppc/spapr.h | 19 +++-
>> 2 files changed, 261 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/ppc/spapr_nvdimm.c b/hw/ppc/spapr_nvdimm.c
>> index 252204e25f..4830eae4a4 100644
>> --- a/hw/ppc/spapr_nvdimm.c
>> +++ b/hw/ppc/spapr_nvdimm.c
>> @@ -35,6 +35,11 @@
>> /* SCM device is unable to persist memory contents */
>> #define PAPR_PMEM_UNARMED PPC_BIT(0)
>>
>> +/* Maximum output buffer size needed to return all nvdimm_perf_stats */
>> +#define SCM_STATS_MAX_OUTPUT_BUFFER (sizeof(struct papr_scm_perf_stats) + \
>> + sizeof(struct papr_scm_perf_stat) * \
>> + ARRAY_SIZE(nvdimm_perf_stats))
>> +
>> bool spapr_nvdimm_validate(HotplugHandler *hotplug_dev, NVDIMMDevice *nvdimm,
>> uint64_t size, Error **errp)
>> {
>> @@ -502,6 +507,243 @@ static target_ulong h_scm_health(PowerPCCPU *cpu, SpaprMachineState *spapr,
>> return H_SUCCESS;
>> }
>>
>> +static int perf_stat_noop(SpaprDrc *drc, uint8_t unused[8], uint64_t *val)
>> +{
>> + *val = 0;
>> + return H_SUCCESS;
>> +}
>> +
>> +static int perf_stat_memlife(SpaprDrc *drc, uint8_t unused[8], uint64_t *val)
>> +{
>> + /* Assume full life available of an NVDIMM right now */
>> + *val = 100;
>
> AFAICT the reporting mechanism makes basically all the stats
> optional. Doesn't it make more sense to omit stats, rather than use
> dummy values in this case? Or is this just an example for the RFC?
>
Yes, this was just an RFC example to illustrate adding support for a new
stat.
>> + return H_SUCCESS;
>> +}
>> +
>> +/*
>> + * Holds all supported performance stats accessors. Each performance-statistic
>> + * is uniquely identified by a 8-byte ascii string for example: 'MemLife '
>> + * which indicate in percentage how much usage life of an nvdimm is remaining.
>> + * 'NoopStat' which is primarily used to test support for retriving performance
>> + * stats and also to replace unknown stats present in the rr-buffer.
>> + *
>> + */
>> +static const struct {
>> + char stat_id[8];
>> + int (*stat_getval)(SpaprDrc *drc, uint8_t id[8], uint64_t *val);
>> +} nvdimm_perf_stats[] = {
>> + { "NoopStat", perf_stat_noop},
>> + { "MemLife ", perf_stat_memlife},
>> +};
>> +
>> +/*
>> + * Given a nvdimm drc and stat-name return its value. In case given stat-name
>> + * isnt supported then return H_PARTIAL.
>> + */
>> +static int nvdimm_stat_getval(SpaprDrc *drc, uint8_t id[8], uint64_t *val)
>> +{
>> + int index;
>> +
>> + /* Lookup the stats-id in the nvdimm_perf_stats table */
>> + for (index = 0; index < ARRAY_SIZE(nvdimm_perf_stats); ++index) {
>> +
>
> No blank line here.
>
Sure, will fix the blank line from this and other places you reported.
>> + if (memcmp(nvdimm_perf_stats[index].stat_id, &id[0], 8) == 0 &&
>> + nvdimm_perf_stats[index].stat_getval) {
>
> I don't see any reason you'd want an entry in the table with a NULL
> function, so I don't think you need both tests.
>
Right. Was being extra cautious here.
>> +
>
> No blank line here either.
>
>> + return nvdimm_perf_stats[index].stat_getval(drc, id, val);
>> + }
>> + }
>> +
>> + return H_PARTIAL;
>> +}
>> +
>> +/*
>> + * Given a request & result buffer header verify its contents. Also
>> + * verify that buffer & buffer-size provided by the guest is accessible and
>> + * large enough to hold the requested stats. The size of buffer needed to
>> + * hold the requested 'num_stat' number of stats is returned in 'size'.
>> + */
>> +static int scm_perf_check_rr_buffer(struct papr_scm_perf_stats *header,
>> + hwaddr addr, size_t *size,
>> + uint32_t *num_stats)
>> +{
>> + size_t expected_buffsize;
>> +
>
> You need to check that size is at least big enough to contain the
> header before accessing the header fields.
>
Yes, the expected_buffsize variable already calculated and checks for
the space needed for for header + space for stats.
>> + /* Verify the header eyecather and version */
>> + if (memcmp(&header->eye_catcher, SCM_STATS_EYECATCHER,
>> + sizeof(header->eye_catcher))) {
>> + return H_BAD_DATA;
>> + }
>> + if (be32_to_cpu(header->stats_version) != 0x1) {
>> + return H_NOT_AVAILABLE;
>> + }
>> +
>> + /* verify that rr buffer has enough space */
>> + *num_stats = be32_to_cpu(header->num_statistics);
>> + if (*num_stats == 0) { /* Return all stats */
>> + expected_buffsize = SCM_STATS_MAX_OUTPUT_BUFFER;
>> + } else { /* Return a subset of stats */
>> + expected_buffsize = sizeof(struct papr_scm_perf_stats) +
>> + (*num_stats) * sizeof(struct papr_scm_perf_stat);
>> +
>> + }
>
> We probably want a hard cap on num_stats as well, so the guest can't
> force up to make arbitrarily large allocations and memory read/writes.
>
Agree. Though the papr spec doesnt provide any upper bound on number of
stats that can be requested, I think a hard cap can be 255 which is the
max number of stats that a 4K page can hold.
>> +
>> + if (*size < expected_buffsize) {
>> + return H_P3;
>> + }
>> + *size = expected_buffsize;
>> +
>> + /* verify that rr buffer is writable */
>> + if (!address_space_access_valid(&address_space_memory, addr, *size,
>> + true, MEMTXATTRS_UNSPECIFIED)) {
>
> Is there any point to this, given that you'll still have to check for
> errors when you go to write back the buffer later?
>
Yes, agree. Will get rid of this check in next iteration.
>> + return H_PRIVILEGE;
>> + }
>> +
>> + return H_SUCCESS;
>> +}
>> +
>> +/*
>> + * For a given DRC index (R3) return one ore more performance stats of an nvdimm
>> + * device in guest allocated Request-and-result buffer (rr-buffer) (R4) of
>> + * given 'size' (R5). The rr-buffer consists of a header described by
>> + * 'struct papr_scm_perf_stats' that embeds the 'stats_version' and
>> + * 'num_statistics' fields. This is followed by an array of
>> + * 'struct papr_scm_perf_stat'. Based on the request type the writes the
>> + * performance into the array of 'struct papr_scm_perf_stat' embedded inside
>> + * the rr-buffer provided by the guest.
>> + * Special cases handled are:
>> + * 'size' == 0 : Return the maximum possible size of rr-buffer
>> + * 'size' != 0 && 'num_statistics == 0' : Return all possible performance stats
>> + *
>> + * In case there was an error fetching a specific stats (e.g stat-id unknown or
>> + * any other error) then return the stat-id in R4 and also replace its stat
>> + * entry in rr-buffer with 'NoopStat'
>> + */
>> +static target_ulong h_scm_performance_stats(PowerPCCPU *cpu,
>> + SpaprMachineState *spapr,
>> + target_ulong opcode,
>> + target_ulong *args)
>> +{
>> + const uint32_t drc_index = args[0];
>> + const hwaddr addr = args[1];
>> + size_t size = args[2];
>> + int index;
>> + MemTxResult result;
>> + uint32_t num_stats;
>> + uint8_t stat_id[8];
>> + unsigned long rc;
>> + uint64_t stat_val, invalid_stat = 0;
>> + struct papr_scm_perf_stats perfstats;
>> + struct papr_scm_perf_stat *stats, *stat;
>> + SpaprDrc *drc = spapr_drc_by_index(drc_index);
>> +
>> + /* Ensure that the drc is valid & is valid PMEM dimm and is plugged in */
>> + if (!drc || !drc->dev ||
>> + spapr_drc_type(drc) != SPAPR_DR_CONNECTOR_TYPE_PMEM) {
>> + return H_PARAMETER;
>> + }
>> +
>> + /* Guest requested max buffer size for output buffer */
>> + if (size == 0) {
>> + args[0] = SCM_STATS_MAX_OUTPUT_BUFFER;
>> + return H_SUCCESS;
>> + }
>> +
>> + /* Read and verify rr-buffer header */
>> + result = address_space_read(&address_space_memory, addr,
>> + MEMTXATTRS_UNSPECIFIED, &perfstats,
>> + sizeof(perfstats));
>
> Ah.. actually you need to check that the provided size is at least big
> enough to cover the header before even reading it here.
>
But that verification is already being done in
scm_perf_check_rr_buffer() as part of header check. In case the provided
buffer is less than sizeof(perfstats) than address_space_read() would
fail or susequently scm_perf_check_rr_buffer() would return an error.
>> + if (result != MEMTX_OK) {
>> + return H_PRIVILEGE;
>> + }
>> +
>> + /* Verify that the rr-buffer is valid */
>> + rc = scm_perf_check_rr_buffer(&perfstats, addr, &size, &num_stats);
>> + if (rc != H_SUCCESS) {
>> + return rc;
>> + }
>> +
>> + /* allocate enough buffer space locally for holding all stats */
>> + stats = g_malloc0(size - sizeof(struct papr_scm_perf_stats));
>
> This seems unnecessarily complicated. Why not just allocate a max
> sized temporary buffer every time - it's in the tens of bytes, not
> something that is really a concern from a memory usage point of view.
> You could even put it on the stack.
>
'SCM_STATS_MAX_OUTPUT_BUFFER' is the minimum size of output buffer
needed to hold all the supported nvdimm stats. A guest can always send a
buffer sized larger than 'SCM_STATS_MAX_OUTPUT_BUFFER' where single stat
is requested more than once. In such a case 'bufferSizeInBytes'
(args[2]) received from guest which is a uint64 can be large.
review comment to self: add check for memory allocation failure
>> + if (num_stats == 0) { /* Return all supported stats */
>> +
>
> No blank line here.
>
>> + for (index = 1; index < ARRAY_SIZE(nvdimm_perf_stats); ++index) {
>
> Why is the starting index 1, not 0?
>
Dont want to return noopstat to the guest. 'nvdimm_perf_stat' will
always start with a noopstat descriptor hence want to skip that.
>> + stat = &stats[index - 1];
>> + memcpy(stat_id, &nvdimm_perf_stats[index].stat_id, 8);
>
> I don't see any point to the 'stat_id' variable here.
>
Right, thanks for pointin it out. This lingered from an earlier version
of the patch and I will get it removed.
>> + rc = nvdimm_stat_getval(drc, stat_id, &stat_val);
>
> So, you're using the nvdimm_stat_getval() here in the num_stats==0
> path, which means you're not taking advatage of the fact that you
> don't actually need to search through the table for your getter
> function in this case. I think that's reasonable for its simplicity,
> but in that case you can make it even simpler:
>
> Rather than having separate paths for the num_stats == 0 and the other
> case, just have the num_stats == 0 case fill in the buffer with a
> canned request which asks for each stat in turn. Then continue on to
> the selected stats path.
>
Thanks, will implement something similar in next iteration.
>> +
>> + /* On error add noop stat to rr buffer & save last inval stat-id */
>> + if (rc != H_SUCCESS) {
>> + if (!invalid_stat) {
>> + memcpy(&invalid_stat, &stat_id[0], 8);
>> + }
>> + memcpy(&stat_id, nvdimm_perf_stats[0].stat_id, 8);
>> + stat_val = 0;
>> + }
>> +
>> + memcpy(&stat->statistic_id, stat_id, 8);
>> + stat->statistic_value = cpu_to_be64(stat_val);
>> + }
>> + /* Number of stats returned == perf_stats array size - noop-stat */
>> + num_stats = ARRAY_SIZE(nvdimm_perf_stats) - 1;
>> +
>> + } else { /* Return a subset of requested stats */
>> +
>
> No blank line.
>
>> + /* copy the rr-buffer from the guest memory */
>> + result = address_space_read(&address_space_memory,
>> + addr + sizeof(struct papr_scm_perf_stats),
>> + MEMTXATTRS_UNSPECIFIED, stats,
>> + size - sizeof(struct papr_scm_perf_stats));
>> +
>> + if (result != MEMTX_OK) {
>> + g_free(stats);
>> + return H_PRIVILEGE;
>> + }
>> +
>> + for (index = 0; index < num_stats; ++index) {
>> + stat = &stats[index];
>> + memcpy(&stat_id, &stats->statistic_id, 8);
>
> What's the point of the 'stat_id' temporary?
>
Agree as mentioned earlier. Will remove this in next iteration of this
patch.
>> + rc = nvdimm_stat_getval(drc, stat_id, &stat_val);
>> +
>> + /* On error add noop stat to rr buffer & save last inval stat-id */
>> + if (rc != H_SUCCESS) {
>> + if (!invalid_stat) {
>> + memcpy(&invalid_stat, &stat_id[0], 8);
>> + }
>> + memcpy(&stat_id, nvdimm_perf_stats[0].stat_id, 8);
>
> Why not write back directly to (the qemu copy of) the rr buffer?
>
Sure can do that. Was trying to update qemu rr-buffer at a single
point rather than scattering updates to it at multiple places.
>> + stat_val = 0;
>
>
> You can also avoid the explicit stat_val = 0 if you make
> nvdimm_stat_getval() always zero stat_val on error.
>
Agree. Thanks for the suggestion. Will add this in next iteration.
>> + }
>> +
>> + memcpy(&stat->statistic_id, stat_id, 8);
>
> AFAICT this copy only does something in the failure case.
>
Right
>> + stat->statistic_value = cpu_to_be64(stat_val);
>> + }
>> + }
>> +
>> + /* Update and copy the local rr-buffer header and stats back to guest */
>> + perfstats.num_statistics = cpu_to_be32(num_stats);
>> + result = address_space_write(&address_space_memory, addr,
>> + MEMTXATTRS_UNSPECIFIED, &perfstats,
>> + sizeof(struct papr_scm_perf_stats));
>> + if (result == MEMTX_OK) {
>> + result = address_space_write(&address_space_memory,
>> + addr + sizeof(struct papr_scm_perf_stats),
>> + MEMTXATTRS_UNSPECIFIED, stats,
>> + size - sizeof(struct papr_scm_perf_stats));
>> + }
>> +
>> + /* Cleanup the stats buffer */
>> + g_free(stats);
>> +
>> + if (result) {
>> + return H_PRIVILEGE;
>> + }
>> +
>> + /* Check if there was a failure in fetching any stat */
>> + args[0] = invalid_stat;
>> + return invalid_stat ? H_PARTIAL : H_SUCCESS;
>> +}
>> +
>> static void spapr_scm_register_types(void)
>> {
>> /* qemu/scm specific hcalls */
>> @@ -511,6 +753,7 @@ static void spapr_scm_register_types(void)
>> spapr_register_hypercall(H_SCM_UNBIND_MEM, h_scm_unbind_mem);
>> spapr_register_hypercall(H_SCM_UNBIND_ALL, h_scm_unbind_all);
>> spapr_register_hypercall(H_SCM_HEALTH, h_scm_health);
>> + spapr_register_hypercall(H_SCM_PERFORMANCE_STATS, h_scm_performance_stats);
>> }
>>
>> type_init(spapr_scm_register_types)
>> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
>> index d2b5a9bdf9..4b71b58e00 100644
>> --- a/include/hw/ppc/spapr.h
>> +++ b/include/hw/ppc/spapr.h
>> @@ -326,6 +326,7 @@ struct SpaprMachineState {
>> #define H_P8 -61
>> #define H_P9 -62
>> #define H_OVERLAP -68
>> +#define H_BAD_DATA -70
>> #define H_UNSUPPORTED_FLAG -256
>> #define H_MULTI_THREADS_ACTIVE -9005
>>
>> @@ -539,8 +540,9 @@ struct SpaprMachineState {
>> #define H_SCM_UNBIND_MEM 0x3F0
>> #define H_SCM_UNBIND_ALL 0x3FC
>> #define H_SCM_HEALTH 0x400
>> +#define H_SCM_PERFORMANCE_STATS 0x418
>>
>> -#define MAX_HCALL_OPCODE H_SCM_HEALTH
>> +#define MAX_HCALL_OPCODE H_SCM_PERFORMANCE_STATS
>>
>> /* The hcalls above are standardized in PAPR and implemented by pHyp
>> * as well.
>> @@ -787,6 +789,21 @@ OBJECT_DECLARE_SIMPLE_TYPE(SpaprTceTable, SPAPR_TCE_TABLE)
>> DECLARE_INSTANCE_CHECKER(IOMMUMemoryRegion, SPAPR_IOMMU_MEMORY_REGION,
>> TYPE_SPAPR_IOMMU_MEMORY_REGION)
>>
>> +/* Defs and structs exchanged with guest when reporting drc perf stats */
>> +#define SCM_STATS_EYECATCHER "SCMSTATS"
>> +
>> +struct QEMU_PACKED papr_scm_perf_stat {
>> + uint8_t statistic_id[8];
>> + uint64_t statistic_value;
>> +};
>> +
>> +struct QEMU_PACKED papr_scm_perf_stats {
>> + uint8_t eye_catcher[8]; /* Should be “SCMSTATS” */
>> + uint32_t stats_version; /* Should be 0x01 */
>> + uint32_t num_statistics; /* Number of stats following */
>> + struct papr_scm_perf_stat scm_statistics[]; /* Performance matrics */
>> +};
>> +
>> struct SpaprTceTable {
>> DeviceState parent;
>> uint32_t liobn;
>
> --
> David Gibson | I'll have my music baroque, and my code
> david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
> | _way_ _around_!
> http://www.ozlabs.org/~dgibson
--
Cheers
~ Vaibhav
