On Wed, Sep 27, 2017 at 10:13:33AM +0100, Will Deacon wrote: > On Wed, Sep 27, 2017 at 09:31:41AM +0100, Marc Zyngier wrote: > > On Tue, Sep 26 2017 at 9:45:42 pm BST, Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx> wrote: > > > On Wed, Sep 13, 2017 at 09:08:30PM +0300, Yury Norov wrote: > > >> The Documentation/arm64/memory.txt says: > > >> When using KVM, the hypervisor maps kernel pages in EL2, at a fixed > > >> offset from the kernel VA (top 24bits of the kernel VA set to zero): > > >> > > >> In fact, kernel addresses are transleted to HYP with kern_hyp_va macro, > > >> which has more options, and none of them assumes clearing of top 24bits > > >> of the kernel VA. > > >> > > >> Signed-off-by: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx> > > >> --- > > >> Documentation/arm64/memory.txt | 15 +++++++++------ > > >> 1 file changed, 9 insertions(+), 6 deletions(-) > > >> > > >> diff --git a/Documentation/arm64/memory.txt b/Documentation/arm64/memory.txt > > >> index d7273a5f6456..c39895d7e3a2 100644 > > >> --- a/Documentation/arm64/memory.txt > > >> +++ b/Documentation/arm64/memory.txt > > >> @@ -86,9 +86,12 @@ Translation table lookup with 64KB pages: > > >> +-------------------------------------------------> [63] TTBR0/1 > > >> > > >> > > >> -When using KVM, the hypervisor maps kernel pages in EL2, at a fixed > > >> -offset from the kernel VA (top 24bits of the kernel VA set to zero): > > >> - > > >> -Start End Size Use > > >> ------------------------------------------------------------------------ > > >> -0000004000000000 0000007fffffffff 256GB kernel objects mapped in HYP > > >> +When using KVM without Virtualization Host Extensions, the hypervisor maps > > >> +kernel pages in EL2, at a fixed offset from the kernel VA. Namely, top 16 > > >> +or 25 bits of the kernel VA set to zero depending on ARM64_VA_BITS_48 or > > >> +ARM64_VA_BITS_39 config option selected; or top 17 or 26 bits of the kernel > > >> +VA set to zero if CPU has Reduced HYP mapping offset capability. See > > >> +kern_hyp_va macro. > > > > What is this "Reduced HYP mapping offset capability"? This is the description of ARM64_HYP_OFFSET_LOW capability in arch/arm64/kernel/cpufeature.c > > You're missing the point that the location of the EL2 mapping is > > conditioned by the location of the identity mapping that is used to > > bring up / tear down KVM. You have to express the VA transformation in > > terms of both VA_BITS (and there is more cases than just 39 or 48 bits) > > *and* the idmap address, not to mention the case where KVM's VA_BITS is > > larger than the rest of the kernel. See the extensive blurb in > > kvm_mmu.h. > > > > >> + > > >> +When using KVM with Virtualization Host Extensions, no additional mappings > > >> +created as host kernel already operates in EL2. > > > > This bit is fine. > > FWIW, I was going to queue a simplified version along the lines of the patch > below. > > Will Thanks. Yury > --->8 > > commit dbf7393b7738a0ba0284551e7b6e014cfb100661 > Author: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx> > Date: Wed Sep 13 21:08:30 2017 +0300 > > arm64: fix documentation on kernel pages mappings to HYP VA > > The Documentation/arm64/memory.txt says: > When using KVM, the hypervisor maps kernel pages in EL2, at a fixed > offset from the kernel VA (top 24bits of the kernel VA set to zero): > > In fact, kernel addresses are transleted to HYP with kern_hyp_va macro, > which has more options, and none of them assumes clearing of top 24bits > of the kernel VA. > > Signed-off-by: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx> > [will: removed gory details] > Signed-off-by: Will Deacon <will.deacon@xxxxxxx> > > diff --git a/Documentation/arm64/memory.txt b/Documentation/arm64/memory.txt > index d7273a5f6456..ea9ee39784a2 100644 > --- a/Documentation/arm64/memory.txt > +++ b/Documentation/arm64/memory.txt > @@ -86,9 +86,9 @@ Translation table lookup with 64KB pages: > +-------------------------------------------------> [63] TTBR0/1 > > > -When using KVM, the hypervisor maps kernel pages in EL2, at a fixed > -offset from the kernel VA (top 24bits of the kernel VA set to zero): > +When using KVM without the Virtualization Host Extensions, the hypervisor > +maps kernel pages in EL2 at a fixed offset from the kernel VA. See the > +kern_hyp_va macro for more details. > > -Start End Size Use > ------------------------------------------------------------------------ > -0000004000000000 0000007fffffffff 256GB kernel objects mapped in HYP > +When using KVM with the Virtualization Host Extensions, no additional > +mappings are created, since the host kernel runs directly in EL2.
