io_uring: change ->cqe_cached invariant for CQE32

With IORING_SETUP_CQE32 ->cqe_cached doesn't store a real address but
rather an implicit offset into cqes. Store the real cqe pointer and
increment it accordingly if CQE32.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/1ee1838cba16bed96381a006950b36ba640d998c.1655455613.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: isilence

io_uring/io_uring.c

@@ -701,11 +701,8 @@ struct io_uring_cqe *__io_get_cqe(struct io_ring_ctx *ctx)
 {
 	struct io_rings *rings = ctx->rings;
 	unsigned int off = ctx->cached_cq_tail & (ctx->cq_entries - 1);
-	unsigned int shift = 0;
 	unsigned int free, queued, len;
 
-	if (ctx->flags & IORING_SETUP_CQE32)
-		shift = 1;
 
 	/* userspace may cheat modifying the tail, be safe and do min */
 	queued = min(__io_cqring_events(ctx), ctx->cq_entries);
@@ -715,11 +712,19 @@ struct io_uring_cqe *__io_get_cqe(struct io_ring_ctx *ctx)
 	if (!len)
 		return NULL;
 
-	ctx->cached_cq_tail++;
+	if (ctx->flags & IORING_SETUP_CQE32) {
+		off <<= 1;
+		len <<= 1;
+	}
+
 	ctx->cqe_cached = &rings->cqes[off];
 	ctx->cqe_sentinel = ctx->cqe_cached + len;
+
+	ctx->cached_cq_tail++;
 	ctx->cqe_cached++;
-	return &rings->cqes[off << shift];
+	if (ctx->flags & IORING_SETUP_CQE32)
+		ctx->cqe_cached++;
+	return &rings->cqes[off];
 }
 
 static bool io_fill_cqe_aux(struct io_ring_ctx *ctx,

io_uring/io_uring.h

@@ -22,14 +22,10 @@ static inline struct io_uring_cqe *io_get_cqe(struct io_ring_ctx *ctx)
 	if (likely(ctx->cqe_cached < ctx->cqe_sentinel)) {
 		struct io_uring_cqe *cqe = ctx->cqe_cached;
 
-		if (ctx->flags & IORING_SETUP_CQE32) {
-			unsigned int off = ctx->cqe_cached - ctx->rings->cqes;
-
-			cqe += off;
-		}
-
 		ctx->cached_cq_tail++;
 		ctx->cqe_cached++;
+		if (ctx->flags & IORING_SETUP_CQE32)
+			ctx->cqe_cached++;
 		return cqe;
 	}