diff options
authorIan Munsie <imunsie@au1.ibm.com>2015-07-23 16:43:56 +1000
committerMichael Ellerman <mpe@ellerman.id.au>2015-08-18 19:34:43 +1000
commitd9232a3da8683cd9c9854a858bcca968fe5f3bca (patch)
parentfc9e9cbf4e48f28525edd27e285820988f1a54b1 (diff)
cxl: Add alternate MMIO error handling
userspace programs using cxl currently have to use two strategies for dealing with MMIO errors simultaneously. They have to check every read for a return of all Fs in case the adapter has gone away and the kernel has not yet noticed, and they have to deal with SIGBUS in case the kernel has already noticed, invalidated the mapping and marked the context as failed. In order to simplify things, this patch adds an alternative approach where the kernel will return a page filled with Fs instead of delivering a SIGBUS. This allows userspace to only need to deal with one of these two error paths, and is intended for use in libraries that use cxl transparently and may not be able to safely install a signal handler. This approach will only work if certain constraints are met. Namely, if the application is both reading and writing to an address in the problem state area it cannot assume that a non-FF read is OK, as it may just be reading out a value it has previously written. Further - since only one page is used per context a write to a given offset would be visible when reading the same offset from a different page in the mapping (this only applies within a single context, not between contexts). An application could deal with this by e.g. making sure it also reads from a read-only offset after any reads to a read/write offset. Due to these constraints, this functionality must be explicitly requested by userspace when starting the context by passing in the CXL_START_WORK_ERR_FF flag. Signed-off-by: Ian Munsie <imunsie@au1.ibm.com> Acked-by: Michael Neuling <mikey@neuling.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
4 files changed, 23 insertions, 3 deletions
diff --git a/drivers/misc/cxl/context.c b/drivers/misc/cxl/context.c
index 615842115848..941fda04aa9a 100644
--- a/drivers/misc/cxl/context.c
+++ b/drivers/misc/cxl/context.c
@@ -126,6 +126,18 @@ static int cxl_mmap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
if (ctx->status != STARTED) {
pr_devel("%s: Context not started, failing problem state access\n", __func__);
+ if (ctx->mmio_err_ff) {
+ if (!ctx->ff_page) {
+ ctx->ff_page = alloc_page(GFP_USER);
+ if (!ctx->ff_page)
+ return VM_FAULT_OOM;
+ memset(page_address(ctx->ff_page), 0xff, PAGE_SIZE);
+ }
+ get_page(ctx->ff_page);
+ vmf->page = ctx->ff_page;
+ vma->vm_page_prot = pgprot_cached(vma->vm_page_prot);
+ return 0;
+ }
@@ -257,6 +269,8 @@ static void reclaim_ctx(struct rcu_head *rcu)
struct cxl_context *ctx = container_of(rcu, struct cxl_context, rcu);
+ if (ctx->ff_page)
+ __free_page(ctx->ff_page);
ctx->sstp = NULL;
diff --git a/drivers/misc/cxl/cxl.h b/drivers/misc/cxl/cxl.h
index 6f5386653dae..e7af256f60c5 100644
--- a/drivers/misc/cxl/cxl.h
+++ b/drivers/misc/cxl/cxl.h
@@ -34,7 +34,7 @@ extern uint cxl_verbose;
* Bump version each time a user API change is made, whether it is
* backwards compatible ot not.
-#define CXL_API_VERSION 1
+#define CXL_API_VERSION 2
@@ -418,6 +418,8 @@ struct cxl_context {
/* Used to unmap any mmaps when force detaching */
struct address_space *mapping;
struct mutex mapping_lock;
+ struct page *ff_page;
+ bool mmio_err_ff;
spinlock_t sste_lock; /* Protects segment table entries */
struct cxl_sste *sstp;
diff --git a/drivers/misc/cxl/file.c b/drivers/misc/cxl/file.c
index 57bdb473749f..a30bf285b5bd 100644
--- a/drivers/misc/cxl/file.c
+++ b/drivers/misc/cxl/file.c
@@ -184,6 +184,8 @@ static long afu_ioctl_start_work(struct cxl_context *ctx,
if (work.flags & CXL_START_WORK_AMR)
amr = work.amr & mfspr(SPRN_UAMOR);
+ ctx->mmio_err_ff = !!(work.flags & CXL_START_WORK_ERR_FF);
* We grab the PID here and not in the file open to allow for the case
* where a process (master, some daemon, etc) has opened the chardev on
@@ -538,7 +540,7 @@ int __init cxl_file_init(void)
* If these change we really need to update API. Either change some
* flags or update API version number CXL_API_VERSION.
BUILD_BUG_ON(sizeof(struct cxl_ioctl_start_work) != 64);
BUILD_BUG_ON(sizeof(struct cxl_event_header) != 8);
BUILD_BUG_ON(sizeof(struct cxl_event_afu_interrupt) != 8);
diff --git a/include/uapi/misc/cxl.h b/include/uapi/misc/cxl.h
index 99a8ca15fe64..1e889aa8a36e 100644
--- a/include/uapi/misc/cxl.h
+++ b/include/uapi/misc/cxl.h
@@ -29,8 +29,10 @@ struct cxl_ioctl_start_work {
#define CXL_START_WORK_AMR 0x0000000000000001ULL
#define CXL_START_WORK_NUM_IRQS 0x0000000000000002ULL
+#define CXL_START_WORK_ERR_FF 0x0000000000000004ULL
/* Possible modes that an afu can be in */

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