[PATCH 2/2] [v3] drm/nouveau: expose GSP-RM logging buffers via debugfs
Danilo Krummrich
dakr at redhat.com
Tue Feb 13 16:57:48 UTC 2024
On 2/12/24 22:15, Timur Tabi wrote:
> The LOGINIT, LOGINTR, LOGRM, and LOGPMU buffers are circular buffers
> that have printf-like logs from GSP-RM and PMU encoded in them.
>
> LOGINIT, LOGINTR, and LOGRM are allocated by Nouveau and their DMA
> addresses are passed to GSP-RM during initialization. The buffers are
> required for GSP-RM to initialize properly.
>
> LOGPMU is also allocated by Nouveau, but its contents are updated
> when Nouveau receives an NV_VGPU_MSG_EVENT_UCODE_LIBOS_PRINT RPC from
> GSP-RM. Nouveau then copies the RPC to the buffer.
>
> The messages are encoded as an array of variable-length structures that
> contain the parameters to an NV_PRINTF call. The format string and
> parameter count are stored in a special ELF image that contains only
> logging strings. This image is not currently shipped with the Nvidia
> driver.
>
> There are two methods to extract the logs.
>
> OpenRM tries to load the logging ELF, and if present, parses the log
> buffers in real time and outputs the strings to the kernel console.
>
> Alternatively, and this is the method used by this patch, the buffers
> can be exposed to user space, and a user-space tool (along with the
> logging ELF image) can parse the buffer and dump the logs.
>
> This method has the advantage that it allows the buffers to be parsed
> even when the logging ELF file is not available to the user. However,
> it has the disadvantage the debubfs entries need to remain until the
> driver is unloaded.
>
> The buffers are exposed via debugfs. The debugfs entries must be
> created before GSP-RM is started, to ensure that they are available
> during GSP-RM initialization.
>
> If GSP-RM fails to initialize, then Nouveau immediately shuts down
> the GSP interface. This would normally also deallocate the logging
> buffers, thereby preventing the user from capturing the debug logs.
> To avoid this, the keep-gsp-logging command line parameter can be
> specified. This parmater is marked as *unsafe* (thereby taining the
> kernel) because the DMA buffer and debugfs entries are never
> deallocated, even if the driver unloads. This gives the user the
> time to capture the logs, but it also means that resources can only
> be recovered by a reboot.
>
> An end-user can capture the logs using the following commands:
>
> cp /sys/kernel/debug/dri/<path>/loginit loginit
> cp /sys/kernel/debug/dri/<path>/logrm logrm
> cp /sys/kernel/debug/dri/<path>/logintr logintr
> cp /sys/kernel/debug/dri/<path>/logpmu logpmu
>
> where <path> is the PCI ID of the GPU (e.g. 0000:65:00.0). If
> keep-gsp-logging is specified, then the <path> is the same but with
> -debug appended (e.g. 0000:65:00.0-debug).
>
> Since LOGPMU is not needed for normal GSP-RM operation, it is only
> created if debugfs is available. Otherwise, the
> NV_VGPU_MSG_EVENT_UCODE_LIBOS_PRINT RPCs are ignored.
>
> Signed-off-by: Timur Tabi <ttabi at nvidia.com>
> ---
> v3: reworked r535_gsp_libos_debugfs_init, rebased for drm-next
>
> .../gpu/drm/nouveau/include/nvkm/subdev/gsp.h | 12 +
> .../gpu/drm/nouveau/nvkm/subdev/gsp/r535.c | 215 +++++++++++++++++-
> 2 files changed, 223 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/include/nvkm/subdev/gsp.h b/drivers/gpu/drm/nouveau/include/nvkm/subdev/gsp.h
> index 3fbc57b16a05..2ee44bdf8be7 100644
> --- a/drivers/gpu/drm/nouveau/include/nvkm/subdev/gsp.h
> +++ b/drivers/gpu/drm/nouveau/include/nvkm/subdev/gsp.h
> @@ -5,6 +5,8 @@
> #include <core/falcon.h>
> #include <core/firmware.h>
>
> +#include <linux/debugfs.h>
> +
> #define GSP_PAGE_SHIFT 12
> #define GSP_PAGE_SIZE BIT(GSP_PAGE_SHIFT)
>
> @@ -217,6 +219,16 @@ struct nvkm_gsp {
>
> /* The size of the registry RPC */
> size_t registry_rpc_size;
> +
> + /*
> + * Logging buffers in debugfs. The wrapper objects need to remain
> + * in memory until the dentry is deleted.
> + */
> + struct debugfs_blob_wrapper blob_init;
> + struct debugfs_blob_wrapper blob_intr;
> + struct debugfs_blob_wrapper blob_rm;
> + struct debugfs_blob_wrapper blob_pmu;
> + struct dentry *debugfs_logging_dir;
I think we should not create those from within the nvkm layer, but rather pass
them down through nvkm_device_pci_new().
Lifecycle wise I think we should ensure that removing the Nouveau kernel module
also cleans up those buffers. Even though keep-gsp-logging is considered unsafe,
we shouldn't leak memory.
For instance, can we allocate corresponding buffers in the driver layer, copy
things over and keep those buffers until nouveau_drm_exit()? This would also
avoid exposing those DMA buffers via debugfs.
> };
>
> static inline bool
> diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c b/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c
> index 86b62c7e1229..56209bf81360 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c
> @@ -26,6 +26,7 @@
> #include <subdev/vfn.h>
> #include <engine/fifo/chan.h>
> #include <engine/sec2.h>
> +#include <drm/drm_device.h>
>
> #include <nvfw/fw.h>
>
> @@ -1979,6 +1980,196 @@ r535_gsp_rmargs_init(struct nvkm_gsp *gsp, bool resume)
> return 0;
> }
>
> +#define NV_GSP_MSG_EVENT_UCODE_LIBOS_CLASS_PMU 0xf3d722
> +
> +/**
> + * r535_gsp_msg_libos_print - capture log message from the PMU
> + * @priv: gsp pointer
> + * @fn: function number (ignored)
> + * @repv: pointer to libos print RPC
> + * @repc: message size
> + *
> + * See _kgspRpcUcodeLibosPrint
> + */
> +static int r535_gsp_msg_libos_print(void *priv, u32 fn, void *repv, u32 repc)
> +{
> + struct nvkm_gsp *gsp = priv;
> + struct nvkm_subdev *subdev = &gsp->subdev;
> + struct {
> + u32 ucodeEngDesc;
> + u32 libosPrintBufSize;
> + u8 libosPrintBuf[];
> + } *rpc = repv;
> + unsigned int class = rpc->ucodeEngDesc >> 8;
> +
> + nvkm_debug(subdev, "received libos print from class 0x%x for %u bytes\n",
> + class, rpc->libosPrintBufSize);
> +
> + if (class != NV_GSP_MSG_EVENT_UCODE_LIBOS_CLASS_PMU) {
> + nvkm_warn(subdev,
> + "received libos print from unknown class 0x%x\n",
> + class);
> + return -ENOMSG;
> + }
> + if (rpc->libosPrintBufSize > GSP_PAGE_SIZE) {
> + nvkm_error(subdev, "libos print is too large (%u bytes)\n",
> + rpc->libosPrintBufSize);
> + return -E2BIG;
> +
> + }
> + memcpy(gsp->blob_pmu.data, rpc->libosPrintBuf, rpc->libosPrintBufSize);
> +
> + return 0;
> +}
> +
> +/*
> + * If GSP-RM load fails, then the GSP nvkm object will be deleted, the
> + * logging debugfs entries will be deleted, and it will not be possible to
> + * debug the load failure. The keep_gsp_logging parameter tells Nouveau
> + * not to free these resources, even if the driver is unloading. In this
> + * case, the only recovery is a reboot.
> + */
> +static bool keep_gsp_logging;
> +module_param_unsafe(keep_gsp_logging, bool, 0444);
> +MODULE_PARM_DESC(keep_gsp_logging,
> + "Do not remove the GSP-RM logging debugfs entries upon exit");
> +
> +/**
> + * r535_gsp_libos_debugfs_init - create logging debugfs entries
> + * @gsp: gsp pointer
> + *
> + * Create the debugfs entries. This exposes the log buffers to
> + * userspace so that an external tool can parse it.
> + *
> + * The 'logpmu' contains exception dumps from the PMU. It is written via an
> + * RPC sent from GSP-RM and must be only 4KB. We create it here because it's
> + * only useful if there is a debugfs entry to expose it. If we get the PMU
> + * logging RPC and there is no debugfs entry, the RPC is just ignored.
> + *
> + * The blob_init, blob_rm, and blob_pmu objects can't be transient
> + * because debugfs_create_blob doesn't copy them.
> + *
> + * NOTE: OpenRM loads the logging elf image and prints the log messages
> + * in real-time. We may add that capability in the future, but that
> + * requires loading an ELF images that are not distributed with the driver,
> + * and adding the parsing code to Nouveau.
> + *
> + * Ideally, this should be part of nouveau_debugfs_init(), but that function
> + * is called too late. We really want to create these debugfs entries before
> + * r535_gsp_booter_load() is called, so that if GSP-RM fails to initialize,
> + * there could still be a log to capture.
> + *
> + * If the unsafe command line pararameter 'keep-gsp-logging' is specified,
> + * then the logging buffer and debugfs entries will be retained when the
> + * driver shuts down. This is necessary to debug initialization failures,
> + * because otherwise the buffers will disappear before the logs can be
> + * captured.
> + */
> +static void r535_gsp_libos_debugfs_init(struct nvkm_gsp *gsp)
> +{
> + struct dentry *dir_init, *dir_intr, *dir_rm, *dir_pmu;
> + struct dentry *root, *dir;
> + struct device *dev = gsp->subdev.device->dev;
> +
> + /*
> + * Under normal circumstances, we add our debugfs entries to the dentry
> + * created by the DRM layer when the driver registered. However, this
> + * dentry and everything in it is deleted if GSP fails to initialize.
> + *
> + * If keep-gsp-logging is specified, then a different top-entry dentry
> + * is created and that is used. This dentry is never deleted, even if
> + * the driver exits.
> + */
> + if (keep_gsp_logging) {
> + char temp[64];
> +
> + /* Find the 'dri' root debugfs entry. Every GPU has a dentry under it */
> + root = debugfs_lookup("dri", NULL);
> + if (IS_ERR(root)) {
> + /* No debugfs, or no root dentry for DRM */
> + return;
> + }
> +
> + scnprintf(temp, sizeof(temp), "%s-debug", dev_name(dev));
> + dir = debugfs_create_dir(temp, root);
> + dput(root);
> + if (IS_ERR(dir)) {
> + nvkm_error(&gsp->subdev,
> + "failed to create %s debugfs entry\n", temp);
> + return;
> + }
> +
> + gsp->debugfs_logging_dir = dir;
> + } else {
> + /* Each GPU has a subdir based on its device name, so find it */
> + struct drm_device *drm_dev = dev_get_drvdata(dev);
> +
> + if (!drm_dev || !drm_dev->debugfs_root) {
> + nvkm_error(&gsp->subdev, "could not find debugfs path\n");
> + return;
> + }
> +
> + dir = drm_dev->debugfs_root;
> + }
> +
> + gsp->blob_init.data = gsp->loginit.data;
> + gsp->blob_init.size = gsp->loginit.size;
> + gsp->blob_intr.data = gsp->logintr.data;
> + gsp->blob_intr.size = gsp->logintr.size;
> + gsp->blob_rm.data = gsp->logrm.data;
> + gsp->blob_rm.size = gsp->logrm.size;
> +
> + /*
> + * Since the PMU buffer is copied from an RPC, it doesn't need to be
> + * a DMA buffer.
> + */
> + gsp->blob_pmu.size = GSP_PAGE_SIZE;
> + gsp->blob_pmu.data = kzalloc(gsp->blob_pmu.size, GFP_KERNEL);
> + if (!gsp->blob_pmu.data)
> + goto error;
> +
> + dir_init = debugfs_create_blob("loginit", 0444, dir, &gsp->blob_init);
> + if (IS_ERR(dir_init)) {
> + nvkm_error(&gsp->subdev, "failed to create loginit debugfs entry\n");
> + goto error;
> + }
> +
> + dir_intr = debugfs_create_blob("logintr", 0444, dir, &gsp->blob_intr);
> + if (IS_ERR(dir_intr)) {
> + nvkm_error(&gsp->subdev, "failed to create logintr debugfs entry\n");
> + goto error;
> + }
> +
> + dir_rm = debugfs_create_blob("logrm", 0444, dir, &gsp->blob_rm);
> + if (IS_ERR(dir_rm)) {
> + nvkm_error(&gsp->subdev, "failed to create logrm debugfs entry\n");
> + goto error;
> + }
> +
> + dir_pmu = debugfs_create_blob("logpmu", 0444, dir, &gsp->blob_pmu);
> + if (IS_ERR(dir_pmu)) {
> + nvkm_error(&gsp->subdev, "failed to create logpmu debugfs entry\n");
> + goto error;
> + }
> +
> + i_size_write(d_inode(dir_init), gsp->blob_init.size);
> + i_size_write(d_inode(dir_intr), gsp->blob_intr.size);
> + i_size_write(d_inode(dir_rm), gsp->blob_rm.size);
> + i_size_write(d_inode(dir_pmu), gsp->blob_pmu.size);
> +
> + r535_gsp_msg_ntfy_add(gsp, 0x0000100C, r535_gsp_msg_libos_print, gsp);
> +
> + nvkm_debug(&gsp->subdev, "created debugfs GSP-RM logging entries\n");
> + return;
> +
> +error:
> + debugfs_remove(gsp->debugfs_logging_dir);
> + gsp->debugfs_logging_dir = NULL;
> +
> + kfree(gsp->blob_pmu.data);
> + gsp->blob_pmu.data = NULL;
> +}
> +
> static inline u64
> r535_gsp_libos_id8(const char *name)
> {
> @@ -2029,7 +2220,11 @@ static void create_pte_array(u64 *ptes, dma_addr_t addr, size_t size)
> * written to directly by GSP-RM and can be any multiple of GSP_PAGE_SIZE.
> *
> * The physical address map for the log buffer is stored in the buffer
> - * itself, starting with offset 1. Offset 0 contains the "put" pointer.
> + * itself, starting with offset 1. Offset 0 contains the "put" pointer (pp).
> + * Initially, pp is equal to 0. If the buffer has valid logging data in it,
> + * then pp points to index into the buffer where the next logging entry will
> + * be written. Therefore, the logging data is valid if:
> + * 1 <= pp < sizeof(buffer)/sizeof(u64)
> *
> * The GSP only understands 4K pages (GSP_PAGE_SIZE), so even if the kernel is
> * configured for a larger page size (e.g. 64K pages), we need to give
> @@ -2100,6 +2295,9 @@ r535_gsp_libos_init(struct nvkm_gsp *gsp)
> args[3].size = gsp->rmargs.size;
> args[3].kind = LIBOS_MEMORY_REGION_CONTIGUOUS;
> args[3].loc = LIBOS_MEMORY_REGION_LOC_SYSMEM;
> +
> + r535_gsp_libos_debugfs_init(gsp);
> +
> return 0;
> }
>
> @@ -2404,9 +2602,18 @@ r535_gsp_dtor(struct nvkm_gsp *gsp)
> r535_gsp_dtor_fws(gsp);
>
> nvkm_gsp_mem_dtor(gsp, &gsp->shm.mem);
> - nvkm_gsp_mem_dtor(gsp, &gsp->loginit);
> - nvkm_gsp_mem_dtor(gsp, &gsp->logintr);
> - nvkm_gsp_mem_dtor(gsp, &gsp->logrm);
> +
> + if (keep_gsp_logging && gsp->debugfs_logging_dir)
> + nvkm_warn(&gsp->subdev,
> + "GSP-RM logging buffers retained, reboot required to recover\n");
> + else {
> + kfree(gsp->blob_pmu.data);
> + gsp->blob_pmu.data = NULL;
> +
> + nvkm_gsp_mem_dtor(gsp, &gsp->loginit);
> + nvkm_gsp_mem_dtor(gsp, &gsp->logintr);
> + nvkm_gsp_mem_dtor(gsp, &gsp->logrm);
> + }
> }
>
> int
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