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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Feb 10, 2020 at 06:03:28PM +0000, Mark Rutland wrote: > On Mon, Feb 10, 2020 at 05:52:15PM +0000, Will Deacon wrote: > > On Mon, Feb 10, 2020 at 05:18:58PM +0000, James Morse wrote: > > > On 28/01/2020 18:49, Sami Tolvanen wrote: > > > > Filter out CC_FLAGS_SCS and -ffixed-x18 for code that runs at a > > > > different exception level. > > > > > > Hmmm, there are two things being disabled here. > > > > > > Stashing the lr in memory pointed to by VA won't work transparently at EL2 ... but > > > shouldn't KVM's C code still treat x18 as a fixed register? > > > > My review of v6 suggested dropping the -ffixed-x18 as well, since it's only > > introduced by SCS (in patch 5) and so isn't required by anything else. Why > > do you think it's needed? > > When EL1 code calls up to hyp, it expects x18 to be preserved across the > call, so hyp needs to either preserve it explicitly across a transitions > from/to EL1 or always preserve it. I thought we explicitly saved/restored it across the call after af12376814a5 ("arm64: kvm: stop treating register x18 as caller save"). Is that not sufficient? > The latter is easiest since any code used by VHE hyp code will need x18 > saved anyway (ans so any common hyp code needs to). I would personally prefer to split the VHE and non-VHE code so they can be compiled with separate options. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel