Mark, and team,
Before going upstream (specifically to Greg), we would like your opinion on the following issue:
PAGE_TABLE_ISOLATION feature - to mitigate meltdown - is not enabled by default for i686 (X32) mainly because it depends on HIGHMEM and X86_PAE.
X86_PAE is NOT default on x86 32bit compilations and it gets only automatically selected if HIGHMEM64G is set (which would justify its need).
With that, right now, all 32-bit kernels generated with default config options are susceptible to meltdown vulnerability (https://bugs.linaro.org/show_bug.cgi?id=4135).
We are thinking on enabling CONFIG_PAGE_TABLE_ISOLATION (w/ CONFIG_X86_PAE and CONFIG_HIGHMEM64G options) for our x86 32-bit builds, but we aren't sure if we should ask upstream to consider the same, since X86_PAE does not look like something that should be default.
What do you think ? Thanks for your inputs!
Rafael