powerpc/pseries: Add papr-platform-dump character driver for dump retrieval

JIRA: https://issues.redhat.com/browse/RHEL-101977

commit 8aa9efc
Author: Haren Myneni <haren@linux.ibm.com>
Date:   Wed Apr 16 15:57:41 2025 -0700

    powerpc/pseries: Add papr-platform-dump character driver for dump retrieval

    ibm,platform-dump RTAS call in combination with writable mapping
    /dev/mem is issued to collect platform dump from the hypervisor
    and may need multiple calls to get the complete dump. The current
    implementation uses rtas_platform_dump() API provided by librtas
    library to issue these RTAS calls. But /dev/mem access by the
    user space is prohibited under system lockdown.

    The solution should be to restrict access to RTAS function in user
    space and provide kernel interfaces to collect dump. This patch
    adds papr-platform-dump character driver and expose standard
    interfaces such as open / ioctl/ read to user space in ways that
    are compatible with lockdown.

    PAPR (7.3.3.4.1 ibm,platform-dump) provides a method to obtain
    the complete dump:
    - Each dump will be identified by ID called dump tag.
    - A sequence of RTAS calls have to be issued until retrieve the
      complete dump. The hypervisor expects the first RTAS call with
      the sequence 0 and the subsequent calls with the sequence
      number returned from the previous calls.
    - The hypervisor returns "dump complete" status once the complete
      dump is retrieved. But expects one more RTAS call from the
      partition with the NULL buffer to invalidate dump which means
      the dump will be removed in the hypervisor.
    - Sequence of calls are allowed with different dump IDs at the
      same time but not with the same dump ID.

    Expose these interfaces to user space with a /dev/papr-platform-dump
    character device using the following programming model:

       int devfd = open("/dev/papr-platform-dump", O_RDONLY);
       int fd = ioctl(devfd,PAPR_PLATFORM_DUMP_IOC_CREATE_HANDLE, &dump_id)
            - Restrict user space to access with the same dump ID.
              Typically we do not expect user space requests the dump
              again for the same dump ID.
       char *buf = malloc(size);
       length = read(fd, buf, size);
            - size should be minimum 1K based on PAPR and  <= 4K based
              on RTAS work area size. It will be restrict to RTAS work
              area size. Using 4K work area based on the current
              implementation in librtas library
            - Each read call issue RTAS call to get the data based on
              the size requirement and returns bytes returned from the
              hypervisor
            - If the previous call returns dump complete status, the
              next read returns 0 like EOF.
       ret = ioctl(PAPR_PLATFORM_DUMP_IOC_INVALIDATE, &dump_id)
            - RTAS call with NULL buffer to invalidates the dump.

    The read API should use the file descriptor obtained from ioctl
    based on dump ID so that gets dump contents for the corresponding
    dump ID. Implemented support in librtas (rtas_platform_dump()) for
    this new ABI to support system lockdown.

    Signed-off-by: Haren Myneni <haren@linux.ibm.com>
    Tested-by: Sathvika Vasireddy <sv@linux.ibm.com>
    Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
    Link: https://patch.msgid.link/20250416225743.596462-7-haren@linux.ibm.com

Signed-off-by: Mamatha Inamdar <minamdar@redhat.com>

Author: Mamatha Inamdar

Documentation/userspace-api/ioctl/ioctl-number.rst

@@ -366,6 +366,8 @@ Code  Seq#    Include File                                           Comments
                                                                      <mailto:linuxppc-dev>
 0xB2  03-05 arch/powerpc/include/uapi/asm/papr-indices.h             powerpc/pseries indices API
                                                                      <mailto:linuxppc-dev>
+0xB2  06-07 arch/powerpc/include/uapi/asm/papr-platform-dump.h       powerpc/pseries Platform Dump API
+                                                                     <mailto:linuxppc-dev>
 0xB3  00     linux/mmc/ioctl.h
 0xB4  00-0F  linux/gpio.h                                            <mailto:linux-gpio@vger.kernel.org>
 0xB5  00-0F  uapi/linux/rpmsg.h                                      <mailto:linux-remoteproc@vger.kernel.org>

arch/powerpc/include/uapi/asm/papr-platform-dump.h

@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_PAPR_PLATFORM_DUMP_H_
+#define _UAPI_PAPR_PLATFORM_DUMP_H_
+
+#include <asm/ioctl.h>
+#include <asm/papr-miscdev.h>
+
+/*
+ * ioctl for /dev/papr-platform-dump. Returns a platform-dump handle fd
+ * corresponding to dump tag.
+ */
+#define PAPR_PLATFORM_DUMP_IOC_CREATE_HANDLE _IOW(PAPR_MISCDEV_IOC_ID, 6, __u64)
+#define PAPR_PLATFORM_DUMP_IOC_INVALIDATE    _IOW(PAPR_MISCDEV_IOC_ID, 7, __u64)
+
+#endif /* _UAPI_PAPR_PLATFORM_DUMP_H_ */

arch/powerpc/platforms/pseries/Makefile

@@ -4,6 +4,7 @@ ccflags-$(CONFIG_PPC_PSERIES_DEBUG)	+= -DDEBUG
 obj-y			:= lpar.o hvCall.o nvram.o reconfig.o \
 			   of_helpers.o rtas-work-area.o papr-sysparm.o \
 			   papr-rtas-common.o papr-vpd.o papr-indices.o \
+			   papr-platform-dump.o \
 			   setup.o iommu.o event_sources.o ras.o \
 			   firmware.o power.o dlpar.o mobility.o rng.o \
 			   pci.o pci_dlpar.o eeh_pseries.o msi.o \