misc: fastrpc: fix remote page size calculation

Remote page size should be calculated based on address and size, fix this!
Without this we will endup with one page less in cases where the buffer
is across 3 pages.

Fixes: c68cfb71 ("misc: fastrpc: Add support for context Invoke method")
Reported-by: Krishnaiah Tadakamalla <ktadakam@qti.qualcomm.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/fastrpc.c

@@ -712,6 +712,7 @@ static int fastrpc_get_args(u32 kernel, struct fastrpc_invoke_ctx *ctx)
 	struct fastrpc_phy_page *pages;
 	int inbufs, i, oix, err = 0;
 	u64 len, rlen, pkt_size;
+	u64 pg_start, pg_end;
 	uintptr_t args;
 	int metalen;
 
@@ -751,8 +752,6 @@ static int fastrpc_get_args(u32 kernel, struct fastrpc_invoke_ctx *ctx)
 		if (!len)
 			continue;
 
-		pages[i].size = roundup(len, PAGE_SIZE);
-
 		if (ctx->maps[i]) {
 			struct vm_area_struct *vma = NULL;
 
@@ -764,6 +763,11 @@ static int fastrpc_get_args(u32 kernel, struct fastrpc_invoke_ctx *ctx)
 				pages[i].addr += ctx->args[i].ptr -
 						 vma->vm_start;
 
+			pg_start = (ctx->args[i].ptr & PAGE_MASK) >> PAGE_SHIFT;
+			pg_end = ((ctx->args[i].ptr + len - 1) & PAGE_MASK) >>
+				  PAGE_SHIFT;
+			pages[i].size = (pg_end - pg_start + 1) * PAGE_SIZE;
+
 		} else {
 
 			if (ctx->olaps[oix].offset == 0) {
@@ -782,6 +786,9 @@ static int fastrpc_get_args(u32 kernel, struct fastrpc_invoke_ctx *ctx)
 					(pkt_size - rlen);
 			pages[i].addr = pages[i].addr &	PAGE_MASK;
 
+			pg_start = (args & PAGE_MASK) >> PAGE_SHIFT;
+			pg_end = ((args + len - 1) & PAGE_MASK) >> PAGE_SHIFT;
+			pages[i].size = (pg_end - pg_start + 1) * PAGE_SIZE;
 			args = args + mlen;
 			rlen -= mlen;
 		}