From b0252cec4a96fea28faa85c47ab0f5d5997444ad Mon Sep 17 00:00:00 2001 From: George Dunlap Date: Fri, 30 Sep 2016 15:42:56 +0100 Subject: [PATCH] xen/trace: Fix trace metadata page count calculation (revert fbf96e6) Changeset fbf96e6, "xentrace: correct formula to calculate t_info_pages", broke the trace metadata page count calculation, by mistaking t_info_first_offset as denominated in bytes, when in fact it is denominated in words (uint32_t). Effectively revert that change, and put a comment there to reduce the chance that someone will make that mistake in the future. Spotted-by: Igor Druzhinin Signed-off-by: George Dunlap --- CC: Olaf Hering CC: Andrew Cooper CC: Jan Beulich --- xen/common/trace.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/xen/common/trace.c b/xen/common/trace.c index f651cf3..2f4ecca 100644 --- a/xen/common/trace.c +++ b/xen/common/trace.c @@ -148,8 +148,12 @@ static int calculate_tbuf_size(unsigned int pages, uint16_t t_info_first_offset) pages = max_pages; } - t_info_words = num_online_cpus() * pages * sizeof(uint32_t); - t_info_pages = PFN_UP(t_info_first_offset + t_info_words); + /* + * NB this calculation is correct, because t_info_first_offset is + * in words, not bytes, not bytes + */ + t_info_words = num_online_cpus() * pages + t_info_first_offset; + t_info_pages = PFN_UP(t_info_words * sizeof(uint32_t)); printk(XENLOG_INFO "xentrace: requesting %u t_info pages " "for %u trace pages on %u cpus\n", t_info_pages, pages, num_online_cpus()); -- 2.1.4