Date: Sat, 7 Dec 2019 13:58:25 +1030 From: "O'Connor, Daniel" <darius@dons.net.au> To: Konstantin Belousov <kostikbel@gmail.com> Cc: freebsd-stable <freebsd-stable@freebsd.org> Subject: Re: Disabling speculative execution mitigations Message-ID: <BA7092AF-29E4-4B7B-B8D6-5CD76D99CD4A@dons.net.au> In-Reply-To: <20191206142221.GL2744@kib.kiev.ua> References: <C19DE24E-22CB-4E55-95CE-0A07FC8A23F5@dons.net.au> <20191206142221.GL2744@kib.kiev.ua>
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> On 7 Dec 2019, at 00:52, Konstantin Belousov <kostikbel@gmail.com> = wrote: >=20 > On Fri, Dec 06, 2019 at 03:51:04PM +1030, O'Connor, Daniel wrote: >> Hi, >> I am trying to track down a performance drop with the ASPEED xorg = video driver between FreeBSD 11 and 12 (I'm not expecting miracles from = it but it was basically unusable..) >>=20 >> I wondered if some of the speculative execution mitigations could be = causing the problem so I did some digging and found these.. >>=20 >> vm.pmap.pti=3D"0" # Disable page table isolation >> hw.ibrs_disable=3D"1" # Disable Indirect Branch Restricted = Speculation > This line enables IBRS. Oops, thanks. >> hw.mds_disable=3D"0" # Disable Microarchitectural Data Sampling = flush >> hw.vmm.vmx=3D"1" # Don't flush RSB on vmexit (presumably only = affects bhyve etc) > I have no idea what this line should configure. It should have been.. hw.vmm.vmx.no_flush_rsb=3D"1" Not that it would affect my test system since I'm not use vmm.ko >> hw.lazy_fpu_switch=3D"1" # Lazily flush FPU >>=20 >> Does anyone know of any others? > Did you read security(7) (on HEAD)? Nope, I didn't even know it existed. Basically, I went through the MFCs listed at = https://wiki.freebsd.org/SpeculativeExecutionVulnerabilities and looked = for tuneables and sysctls. With respect to the man page, I find it difficult to know what a given = value for each sysctl will do, as evidenced by my confusion above about = IBRS. -- Daniel O'Connor "The nice thing about standards is that there are so many of them to choose from." -- Andrew Tanenbaum
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