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    SubjectRe: [PATCH v2 07/21] arm64: KVM: VHE: Patch out kern_hyp_va
    On Mon, Jan 25, 2016 at 03:53:41PM +0000, Marc Zyngier wrote:
    > The kern_hyp_va macro is pretty meaninless with VHE, as there is
    > only one mapping - the kernel one.
    >
    > In order to keep the code readable and efficient, use runtime
    > patching to replace the 'and' instruction used to compute the VA
    > with a 'nop'.
    >
    > Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
    > ---
    > arch/arm64/include/asm/kvm_mmu.h | 11 ++++++++++-
    > arch/arm64/kvm/hyp/hyp.h | 25 ++++++++++++++++++++++---
    > 2 files changed, 32 insertions(+), 4 deletions(-)
    >
    > diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
    > index d3e6d7b..62f0d14 100644
    > --- a/arch/arm64/include/asm/kvm_mmu.h
    > +++ b/arch/arm64/include/asm/kvm_mmu.h
    > @@ -23,13 +23,16 @@
    > #include <asm/cpufeature.h>
    >
    > /*
    > - * As we only have the TTBR0_EL2 register, we cannot express
    > + * As ARMv8.0 only has the TTBR0_EL2 register, we cannot express
    > * "negative" addresses. This makes it impossible to directly share
    > * mappings with the kernel.
    > *
    > * Instead, give the HYP mode its own VA region at a fixed offset from
    > * the kernel by just masking the top bits (which are all ones for a
    > * kernel address).
    > + *
    > + * ARMv8.1 (using VHE) does have a TTBR1_EL2, and doesn't use these
    > + * macros (the entire kernel runs at EL2).
    > */
    > #define HYP_PAGE_OFFSET_SHIFT VA_BITS
    > #define HYP_PAGE_OFFSET_MASK ((UL(1) << HYP_PAGE_OFFSET_SHIFT) - 1)
    > @@ -56,6 +59,8 @@
    >
    > #ifdef __ASSEMBLY__
    >
    > +#include <asm/alternative.h>
    > +#include <asm/cpufeature.h>
    > #include <asm/kvm_arm.h>
    >
    > .macro setup_vtcr tmp1, tmp2
    > @@ -84,7 +89,11 @@
    > * reg: VA to be converted.
    > */
    > .macro kern_hyp_va reg
    > +alternative_if_not ARM64_HAS_VIRT_HOST_EXTN
    > and \reg, \reg, #HYP_PAGE_OFFSET_MASK
    > +alternative_else
    > + nop
    > +alternative_endif
    > .endm
    >
    > #else
    > diff --git a/arch/arm64/kvm/hyp/hyp.h b/arch/arm64/kvm/hyp/hyp.h
    > index fb27517..fc502f3 100644
    > --- a/arch/arm64/kvm/hyp/hyp.h
    > +++ b/arch/arm64/kvm/hyp/hyp.h
    > @@ -25,9 +25,28 @@
    >
    > #define __hyp_text __section(.hyp.text) notrace
    >
    > -#define kern_hyp_va(v) (typeof(v))((unsigned long)(v) & HYP_PAGE_OFFSET_MASK)
    > -#define hyp_kern_va(v) (typeof(v))((unsigned long)(v) - HYP_PAGE_OFFSET \
    > - + PAGE_OFFSET)
    > +static inline unsigned long __kern_hyp_va(unsigned long v)
    > +{
    > + asm volatile(ALTERNATIVE("and %0, %0, %1",
    > + "nop",
    > + ARM64_HAS_VIRT_HOST_EXTN)
    > + : "+r" (v) : "i" (HYP_PAGE_OFFSET_MASK));
    > + return v;
    > +}
    > +
    > +#define kern_hyp_va(v) (typeof(v))(__kern_hyp_va((unsigned long)(v)))
    > +
    > +static inline unsigned long __hyp_kern_va(unsigned long v)
    > +{
    > + u64 offset = PAGE_OFFSET - HYP_PAGE_OFFSET;
    > + asm volatile(ALTERNATIVE("add %0, %0, %1",
    > + "nop",
    > + ARM64_HAS_VIRT_HOST_EXTN)
    > + : "+r" (v) : "r" (offset));
    > + return v;
    > +}
    > +
    > +#define hyp_kern_va(v) (typeof(v))(__hyp_kern_va((unsigned long)(v)))

    why do we need this casting of values instead of just defining these
    inlines and calling them directly with proper typing?

    -Christoffer

    >
    > /**
    > * hyp_alternate_select - Generates patchable code sequences that are
    > --
    > 2.1.4
    >

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