On Wed, Sep 27 2017 at 10:13:33 am BST, Will Deacon <will.deacon@xxxxxxx> 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"? >> >> 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 > > --->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. Acked-by: Marc Zyngier <marc.zyngier@xxxxxxx> M. -- Jazz is not dead. It just smells funny. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
