RE: [PATCH v5 03/12] x86/mm: consolidate full flush threshold decision

Michael Kelley
2025-01-17T19:23:10Z

From: riel@surriel.com <riel@surriel.com> Sent: Wednesday, January 15, 2025 6:30 PM
>
> Reduce code duplication by consolidating the decision point
> for whether to do individual invalidations or a full flush
> inside get_flush_tlb_info.
>
> Signed-off-by: Rik van Riel <riel@surriel.com>
> Suggested-by: Dave Hansen <dave.hansen@intel.com>
> ---
> arch/x86/mm/tlb.c | 43 ++++++++++++++++++++-----------------------
> 1 file changed, 20 insertions(+), 23 deletions(-)
>
> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
> index 6cf881a942bb..2f38cf95dee3 100644
> --- a/arch/x86/mm/tlb.c
> +++ b/arch/x86/mm/tlb.c

[snip]

> @@ -1089,22 +1089,19 @@ static void do_kernel_range_flush(void *info)
>
> void flush_tlb_kernel_range(unsigned long start, unsigned long end)
> {
> - /* Balance as user space task's flush, a bit conservative */
> - if (end == TLB_FLUSH_ALL ||
> - (end - start) > tlb_single_page_flush_ceiling << PAGE_SHIFT) {
> - on_each_cpu(do_flush_tlb_all, NULL, 1);
> - } else {
> - struct flush_tlb_info *info;
> + struct flush_tlb_info *info;
>
> - preempt_disable();
> - info = get_flush_tlb_info(NULL, start, end, 0, false,
> - TLB_GENERATION_INVALID);
> + guard(preempt)();
> +
> + info = get_flush_tlb_info(NULL, start, end, PAGE_SHIFT, false,
> + TLB_GENERATION_INVALID);
>
> + if (end == TLB_FLUSH_ALL)

This needs to test "info->end", not "end".

In my VM on Hyper-V *without* INVLPGB support, the bug causes
boot to hang as it tries to individually flush each page in the
[0, TLB_FLUSH_ALL] range. :-)

Michael

> + on_each_cpu(do_flush_tlb_all, NULL, 1);
> + else
> on_each_cpu(do_kernel_range_flush, info, 1);
>
> - put_flush_tlb_info();
> - preempt_enable();
> - }
> + put_flush_tlb_info();
> }
>
> /*