From 13ba0aec9c83e0a060ca976eace71414d4b1ca8d Mon Sep 17 00:00:00 2001
From: Kalesh Singh <kaleshsingh@google.com>
Date: Fri, 4 Oct 2024 16:00:19 -0700
Subject: [PATCH] ANDROID: 16K: Fixup perf_mmap check for metadata page

perf_mmap() expects a power of 2 number of pages plus 1 additional page.

In the emulated __PAGE_SIZE case, the one extra page is actually
  (__PAGE_SIZE / PAGE_SIZE) number of 4KiB pages in the kernel.

See MMAP layout in perf_event_open():

       The mmap size should be 1+2^n pages, where the first page is a
       metadata page (struct perf_event_mmap_page) that contains various
       bits of information such as where the ring-buffer head is. [1]

Also update perf_event_mmap_kb's default value to reflect this;
    i.e 512KiB + sizeof 1 page in KiB (__PAGE_SIZE/1024)

[1] https://man7.org/linux/man-pages/man2/perf_event_open.2.html

Bug: 383389337
Bug: 366098040
Test: atest vts_ltp_test_x86_64
Change-Id: I475e3c9ed896d8e3735681b1143e31c62ed20359
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
---
 kernel/events/core.c  |  5 +++--
 mm/page_size_compat.c | 13 +++++++++++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 01cc0f41b411..9bdc322273fd 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -46,6 +46,7 @@
 #include <linux/filter.h>
 #include <linux/namei.h>
 #include <linux/parser.h>
+#include <linux/page_size_compat.h>
 #include <linux/sched/clock.h>
 #include <linux/sched/mm.h>
 #include <linux/proc_ns.h>
@@ -6628,7 +6629,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
 	vma_size = vma->vm_end - vma->vm_start;
 
 	if (vma->vm_pgoff == 0) {
-		nr_pages = (vma_size / PAGE_SIZE) - 1;
+		nr_pages = (vma_size / PAGE_SIZE) - (__PAGE_SIZE / PAGE_SIZE);
 	} else {
 		/*
 		 * AUX area mapping: if rb->aux_nr_pages != 0, it's already
@@ -6699,7 +6700,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
 	if (nr_pages != 0 && !is_power_of_2(nr_pages))
 		return -EINVAL;
 
-	if (vma_size != PAGE_SIZE * (1 + nr_pages))
+	if (vma_size != PAGE_SIZE * ((__PAGE_SIZE / PAGE_SIZE) + nr_pages))
 		return -EINVAL;
 
 	WARN_ON_ONCE(event->ctx->parent_ctx);
diff --git a/mm/page_size_compat.c b/mm/page_size_compat.c
index 3b2b9f52a42e..716f59f25518 100644
--- a/mm/page_size_compat.c
+++ b/mm/page_size_compat.c
@@ -13,6 +13,7 @@
 #include <linux/pagemap.h>
 #include <linux/page_size_compat.h>
 #include <linux/swap.h>
+#include <linux/perf_event.h>
 
 #define MIN_PAGE_SHIFT_COMPAT (PAGE_SHIFT + 1)
 #define MAX_PAGE_SHIFT_COMPAT 16 /* Max of 64KB */
@@ -315,3 +316,15 @@ free_magic:
 
 	return error;
 }
+
+static int __init init_sysctl_perf_event_mlock(void)
+{
+	if (!static_branch_unlikely(&page_shift_compat_enabled))
+		return 0;
+
+	/* Minimum for 512 kiB + 1 user control page */
+	sysctl_perf_event_mlock = 512 + (__PAGE_SIZE / 1024); /* 'free' kiB per user */
+
+	return 0;
+}
+core_initcall(init_sysctl_perf_event_mlock);