Re: [PATCH] kexec-tools: ppc64: avoid adding coherent memory regions to crash memory ranges

[Alistair Popple <alistair@popple.id.au>]

Hi,

I haven't reviewed the code in depth but skipping memory regions marked
ibm,coherent-device-memory is the right thing to do as the links to this memory
will usually go down prior during a kexec.

Also device-drivers typically put this memory into ZONE_MOVABLE which means
there will be no kernel allocations present in this memory.

Regards,

Alistair

On Thu, 17 Aug 2017 06:01:51 PM Hari Bathini wrote:
> Accelerator devices like GPU and FPGA cards contain onboard memory. This
> onboard memory is represented as a memory only NUMA node, integrating it
> with core memory subsystem. Since, the link through which these devices
> are integrated to core memory goes down after a system crash and they are
> meant for user workloads, avoid adding coherent device memory regions to
> crash memory ranges. Without this change, makedumpfile tool tries to save
> unaccessible coherent device memory regions, crashing the system.
> 
> Signed-off-by: Hari Bathini <hbathini@linux.vnet.ibm.com>
> ---
>  kexec/arch/ppc64/crashdump-ppc64.c |   64 +++++++++++++++++++++++++++++++++++-
>  kexec/arch/ppc64/kexec-ppc64.h     |    1 +
>  2 files changed, 63 insertions(+), 2 deletions(-)
> 
> diff --git a/kexec/arch/ppc64/crashdump-ppc64.c b/kexec/arch/ppc64/crashdump-ppc64.c
> index 13995bf..7ea3983 100644
> --- a/kexec/arch/ppc64/crashdump-ppc64.c
> +++ b/kexec/arch/ppc64/crashdump-ppc64.c
> @@ -181,6 +181,53 @@ static int get_dyn_reconf_crash_memory_ranges(void)
>  	return 0;
>  }
>  
> +/*
> + * For a given memory node, check if it is mapped to system RAM or
> + * to onboard memory on accelerator device like GPU card or such.
> + */
> +static int is_coherent_device_mem(const char *fname)
> +{
> +	char fpath[PATH_LEN];
> +	char buf[32];
> +	DIR *dmem;
> +	FILE *file;
> +	struct dirent *mentry;
> +	int cnt, ret = 0;
> +
> +	strcpy(fpath, fname);
> +	if ((dmem = opendir(fpath)) == NULL) {
> +		perror(fpath);
> +		return -1;
> +	}
> +
> +	while ((mentry = readdir(dmem)) != NULL) {
> +		if (strcmp(mentry->d_name, "compatible"))
> +			continue;
> +
> +		strcat(fpath, "/compatible");
> +		if ((file = fopen(fpath, "r")) == NULL) {
> +			perror(fpath);
> +			ret = -1;
> +			break;
> +		}
> +		if ((cnt = fread(buf, 1, 32, file)) < 0) {
> +			perror(fpath);
> +			fclose(file);
> +			ret = -1;
> +			break;
> +		}
> +		if (!strncmp(buf, "ibm,coherent-device-memory", 26)) {
> +			ret = 1;
> +			break;
> +		}
> +		fclose(file);
> +	}
> +
> +	closedir(dmem);
> +	return ret;
> +}
> +
> +
>  /* Reads the appropriate file and retrieves the SYSTEM RAM regions for whom to
>   * create Elf headers. Keeping it separate from get_memory_ranges() as
>   * requirements are different in the case of normal kexec and crashdumps.
> @@ -196,12 +243,12 @@ static int get_crash_memory_ranges(struct memory_range **range, int *ranges)
>  {
>  
>  	char device_tree[256] = "/proc/device-tree/";
> -	char fname[256];
> +	char fname[PATH_LEN];
>  	char buf[MAXBYTES];
>  	DIR *dir, *dmem;
>  	FILE *file;
>  	struct dirent *dentry, *mentry;
> -	int n, crash_rng_len = 0;
> +	int n, ret, crash_rng_len = 0;
>  	unsigned long long start, end;
>  	int page_size;
>  
> @@ -240,6 +287,19 @@ static int get_crash_memory_ranges(struct memory_range **range, int *ranges)
>  			continue;
>  		strcpy(fname, device_tree);
>  		strcat(fname, dentry->d_name);
> +
> +		ret = is_coherent_device_mem(fname);
> +		if (ret == -1) {
> +			closedir(dir);
> +			goto err;
> +		} else if (ret == 1) {
> +			/*
> +			 * Avoid adding this memory region as it is not
> +			 * mapped to system RAM.
> +			 */
> +			continue;
> +		}
> +
>  		if ((dmem = opendir(fname)) == NULL) {
>  			perror(fname);
>  			closedir(dir);
> diff --git a/kexec/arch/ppc64/kexec-ppc64.h b/kexec/arch/ppc64/kexec-ppc64.h
> index 633ae77..434b4bf 100644
> --- a/kexec/arch/ppc64/kexec-ppc64.h
> +++ b/kexec/arch/ppc64/kexec-ppc64.h
> @@ -1,6 +1,7 @@
>  #ifndef KEXEC_PPC64_H
>  #define KEXEC_PPC64_H
>  
> +#define PATH_LEN 256
>  #define MAXBYTES 128
>  #define MAX_LINE 160
>  #define CORE_TYPE_ELF32 1
> 


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