Hi James, On 12/03/18 18:27, James Morse wrote: > Hi Marc, > > On 01/03/18 15:55, Marc Zyngier wrote: >> So far, the branch from the vector slots to the main vectors can at >> most be 4GB from the main vectors (the reach of ADRP), and this >> distance is known at compile time. If we were to remap the slots >> to an unrelated VA, things would break badly. >> >> A way to achieve VA independence would be to load the absolute >> address of the vectors (__kvm_hyp_vector), either using a constant >> pool or a series of movs, followed by an indirect branch. >> >> This patches implements the latter solution, using another instance >> of a patching callback. > >> diff --git a/arch/arm64/kernel/bpi.S b/arch/arm64/kernel/bpi.S >> index e000cb390618..e8d997788ad0 100644 >> --- a/arch/arm64/kernel/bpi.S >> +++ b/arch/arm64/kernel/bpi.S >> @@ -19,6 +19,9 @@ >> #include <linux/linkage.h> >> #include <linux/arm-smccc.h> >> >> +#include <asm/alternative.h> >> +#include <asm/kvm_mmu.h> >> + >> .macro hyp_ventry offset >> .align 7 >> .rept 29 >> @@ -64,9 +67,15 @@ ENTRY(__bp_harden_hyp_vecs_start) >> .endr >> >> __kvm_enter_vectors: >> +alternative_cb kvm_patch_vector_branch >> + movz x1, #0 >> + movk x1, #0, lsl #16 >> + movk x1, #0, lsl #32 >> + movk x1, #0, lsl #48 >> +alternative_cb_end >> >> - adr_l x1, __kvm_hyp_vector >> add x0, x1, x0 >> + kern_hyp_va x0 > > Can't you patch the kern_hyp_va address into the movk block directly? > Obviously you can't call kern_hyp_va, but you could generate the layout and have > some slow __kern_hyp_va() to generate the value. This would avoid generating a > value, to then throw half of it away and patch something else in. Hmmm. That's pretty twisted. Actually, this is utterly terrifying. And thus absolutely mandatory. Irk. I really like it. > Does this code run for VHE systems too? (it not, is the x<<48 movk needed?) This is indeed VHE only, and if/when I adopt your suggestion, we'll be able to drop the last movk, effectively getting rid of 6 instructions on the exception path. Awesome! Thanks, M. -- Jazz is not dead. It just smells funny...
