| Message ID | 1453737235-16522-7-git-send-email-marc.zyngier@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, Jan 25, 2016 at 03:53:40PM +0000, Marc Zyngier wrote: > With VHE, the host never issues an HVC instruction to get into the > KVM code, as we can simply branch there. > > Use runtime code patching to simplify things a bit. > > Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> > --- > arch/arm64/kvm/hyp.S | 7 +++++++ > arch/arm64/kvm/hyp/hyp-entry.S | 38 +++++++++++++++++++++++++++++--------- > 2 files changed, 36 insertions(+), 9 deletions(-) > > diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S > index 0ccdcbb..0689a74 100644 > --- a/arch/arm64/kvm/hyp.S > +++ b/arch/arm64/kvm/hyp.S > @@ -17,7 +17,9 @@ > > #include <linux/linkage.h> > > +#include <asm/alternative.h> > #include <asm/assembler.h> > +#include <asm/cpufeature.h> > > /* > * u64 kvm_call_hyp(void *hypfn, ...); > @@ -38,6 +40,11 @@ > * arch/arm64/kernel/hyp_stub.S. > */ > ENTRY(kvm_call_hyp) > +alternative_if_not ARM64_HAS_VIRT_HOST_EXTN > hvc #0 > ret > +alternative_else > + b __vhe_hyp_call > + nop > +alternative_endif > ENDPROC(kvm_call_hyp) > diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S > index 93e8d983..9e0683f 100644 > --- a/arch/arm64/kvm/hyp/hyp-entry.S > +++ b/arch/arm64/kvm/hyp/hyp-entry.S > @@ -38,6 +38,32 @@ > ldp x0, x1, [sp], #16 > .endm > > +.macro do_el2_call > + /* > + * Shuffle the parameters before calling the function > + * pointed to in x0. Assumes parameters in x[1,2,3]. > + */ > + stp lr, xzr, [sp, #-16]! remind me why this pair isn't just doing "str" instead of "stp" with the xzr ? > + mov lr, x0 > + mov x0, x1 > + mov x1, x2 > + mov x2, x3 > + blr lr > + ldp lr, xzr, [sp], #16 > +.endm > + > +ENTRY(__vhe_hyp_call) > + do_el2_call > + /* > + * We used to rely on having an exception return to get > + * an implicit isb. In the E2H case, we don't have it anymore. > + * rather than changing all the leaf functions, just do it here > + * before returning to the rest of the kernel. > + */ why is this not the case with an ISB before do_el2_call then? > + isb > + ret > +ENDPROC(__vhe_hyp_call) > + > el1_sync: // Guest trapped into EL2 > save_x0_to_x3 > > @@ -58,19 +84,13 @@ el1_sync: // Guest trapped into EL2 > mrs x0, vbar_el2 > b 2f > > -1: stp lr, xzr, [sp, #-16]! > - > +1: > /* > - * Compute the function address in EL2, and shuffle the parameters. > + * Perform the EL2 call > */ > kern_hyp_va x0 > - mov lr, x0 > - mov x0, x1 > - mov x1, x2 > - mov x2, x3 > - blr lr > + do_el2_call > > - ldp lr, xzr, [sp], #16 > 2: eret > > el1_trap: > -- > 2.1.4 > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 01/02/16 13:16, Christoffer Dall wrote: > On Mon, Jan 25, 2016 at 03:53:40PM +0000, Marc Zyngier wrote: >> With VHE, the host never issues an HVC instruction to get into the >> KVM code, as we can simply branch there. >> >> Use runtime code patching to simplify things a bit. >> >> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> >> --- >> arch/arm64/kvm/hyp.S | 7 +++++++ >> arch/arm64/kvm/hyp/hyp-entry.S | 38 +++++++++++++++++++++++++++++--------- >> 2 files changed, 36 insertions(+), 9 deletions(-) >> >> diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S >> index 0ccdcbb..0689a74 100644 >> --- a/arch/arm64/kvm/hyp.S >> +++ b/arch/arm64/kvm/hyp.S >> @@ -17,7 +17,9 @@ >> >> #include <linux/linkage.h> >> >> +#include <asm/alternative.h> >> #include <asm/assembler.h> >> +#include <asm/cpufeature.h> >> >> /* >> * u64 kvm_call_hyp(void *hypfn, ...); >> @@ -38,6 +40,11 @@ >> * arch/arm64/kernel/hyp_stub.S. >> */ >> ENTRY(kvm_call_hyp) >> +alternative_if_not ARM64_HAS_VIRT_HOST_EXTN >> hvc #0 >> ret >> +alternative_else >> + b __vhe_hyp_call >> + nop >> +alternative_endif >> ENDPROC(kvm_call_hyp) >> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S >> index 93e8d983..9e0683f 100644 >> --- a/arch/arm64/kvm/hyp/hyp-entry.S >> +++ b/arch/arm64/kvm/hyp/hyp-entry.S >> @@ -38,6 +38,32 @@ >> ldp x0, x1, [sp], #16 >> .endm >> >> +.macro do_el2_call >> + /* >> + * Shuffle the parameters before calling the function >> + * pointed to in x0. Assumes parameters in x[1,2,3]. >> + */ >> + stp lr, xzr, [sp, #-16]! > > remind me why this pair isn't just doing "str" instead of "stp" with the > xzr ? Because SP has to be aligned on a 16 bytes boundary at all times. > >> + mov lr, x0 >> + mov x0, x1 >> + mov x1, x2 >> + mov x2, x3 >> + blr lr >> + ldp lr, xzr, [sp], #16 >> +.endm >> + >> +ENTRY(__vhe_hyp_call) >> + do_el2_call >> + /* >> + * We used to rely on having an exception return to get >> + * an implicit isb. In the E2H case, we don't have it anymore. >> + * rather than changing all the leaf functions, just do it here >> + * before returning to the rest of the kernel. >> + */ > > why is this not the case with an ISB before do_el2_call then? That's a good point. I guess the safest thing to do would be to add one, but looking at the various functions we call, I don't see any that could go wrong by not having a ISB in their prologue. Or maybe you've identified such a case? Thanks, M.
On Mon, Feb 01, 2016 at 01:34:16PM +0000, Marc Zyngier wrote: > On 01/02/16 13:16, Christoffer Dall wrote: > > On Mon, Jan 25, 2016 at 03:53:40PM +0000, Marc Zyngier wrote: > >> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S > >> index 93e8d983..9e0683f 100644 > >> --- a/arch/arm64/kvm/hyp/hyp-entry.S > >> +++ b/arch/arm64/kvm/hyp/hyp-entry.S > >> @@ -38,6 +38,32 @@ > >> ldp x0, x1, [sp], #16 > >> .endm > >> > >> +.macro do_el2_call > >> + /* > >> + * Shuffle the parameters before calling the function > >> + * pointed to in x0. Assumes parameters in x[1,2,3]. > >> + */ > >> + stp lr, xzr, [sp, #-16]! > > > > remind me why this pair isn't just doing "str" instead of "stp" with the > > xzr ? > > Because SP has to be aligned on a 16 bytes boundary at all times. You could do something like: sub sp, sp, #16 str lr, [sp]
On Mon, Feb 01, 2016 at 01:34:16PM +0000, Marc Zyngier wrote: > On 01/02/16 13:16, Christoffer Dall wrote: > > On Mon, Jan 25, 2016 at 03:53:40PM +0000, Marc Zyngier wrote: > >> With VHE, the host never issues an HVC instruction to get into the > >> KVM code, as we can simply branch there. > >> > >> Use runtime code patching to simplify things a bit. > >> > >> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> > >> --- > >> arch/arm64/kvm/hyp.S | 7 +++++++ > >> arch/arm64/kvm/hyp/hyp-entry.S | 38 +++++++++++++++++++++++++++++--------- > >> 2 files changed, 36 insertions(+), 9 deletions(-) > >> > >> diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S > >> index 0ccdcbb..0689a74 100644 > >> --- a/arch/arm64/kvm/hyp.S > >> +++ b/arch/arm64/kvm/hyp.S > >> @@ -17,7 +17,9 @@ > >> > >> #include <linux/linkage.h> > >> > >> +#include <asm/alternative.h> > >> #include <asm/assembler.h> > >> +#include <asm/cpufeature.h> > >> > >> /* > >> * u64 kvm_call_hyp(void *hypfn, ...); > >> @@ -38,6 +40,11 @@ > >> * arch/arm64/kernel/hyp_stub.S. > >> */ > >> ENTRY(kvm_call_hyp) > >> +alternative_if_not ARM64_HAS_VIRT_HOST_EXTN > >> hvc #0 > >> ret > >> +alternative_else > >> + b __vhe_hyp_call > >> + nop > >> +alternative_endif > >> ENDPROC(kvm_call_hyp) > >> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S > >> index 93e8d983..9e0683f 100644 > >> --- a/arch/arm64/kvm/hyp/hyp-entry.S > >> +++ b/arch/arm64/kvm/hyp/hyp-entry.S > >> @@ -38,6 +38,32 @@ > >> ldp x0, x1, [sp], #16 > >> .endm > >> > >> +.macro do_el2_call > >> + /* > >> + * Shuffle the parameters before calling the function > >> + * pointed to in x0. Assumes parameters in x[1,2,3]. > >> + */ > >> + stp lr, xzr, [sp, #-16]! > > > > remind me why this pair isn't just doing "str" instead of "stp" with the > > xzr ? > > Because SP has to be aligned on a 16 bytes boundary at all times. > right, duh. > > > >> + mov lr, x0 > >> + mov x0, x1 > >> + mov x1, x2 > >> + mov x2, x3 > >> + blr lr > >> + ldp lr, xzr, [sp], #16 > >> +.endm > >> + > >> +ENTRY(__vhe_hyp_call) > >> + do_el2_call > >> + /* > >> + * We used to rely on having an exception return to get > >> + * an implicit isb. In the E2H case, we don't have it anymore. > >> + * rather than changing all the leaf functions, just do it here > >> + * before returning to the rest of the kernel. > >> + */ > > > > why is this not the case with an ISB before do_el2_call then? > > That's a good point. I guess the safest thing to do would be to add one, > but looking at the various functions we call, I don't see any that could > go wrong by not having a ISB in their prologue. > > Or maybe you've identified such a case? > I think I argued on Mario's VFP patches that we could rely on an ISB before the hyp call, but they're not merged yet, so, hey... -Christoffer -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 01/02/16 15:36, Catalin Marinas wrote: > On Mon, Feb 01, 2016 at 01:34:16PM +0000, Marc Zyngier wrote: >> On 01/02/16 13:16, Christoffer Dall wrote: >>> On Mon, Jan 25, 2016 at 03:53:40PM +0000, Marc Zyngier wrote: >>>> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S >>>> index 93e8d983..9e0683f 100644 >>>> --- a/arch/arm64/kvm/hyp/hyp-entry.S >>>> +++ b/arch/arm64/kvm/hyp/hyp-entry.S >>>> @@ -38,6 +38,32 @@ >>>> ldp x0, x1, [sp], #16 >>>> .endm >>>> >>>> +.macro do_el2_call >>>> + /* >>>> + * Shuffle the parameters before calling the function >>>> + * pointed to in x0. Assumes parameters in x[1,2,3]. >>>> + */ >>>> + stp lr, xzr, [sp, #-16]! >>> >>> remind me why this pair isn't just doing "str" instead of "stp" with the >>> xzr ? >> >> Because SP has to be aligned on a 16 bytes boundary at all times. > > You could do something like: > > sub sp, sp, #16 > str lr, [sp] > Ah, fair enough. I'll fold that in. Thanks, M.
On 1 February 2016 at 17:20, Marc Zyngier <marc.zyngier@arm.com> wrote: > On 01/02/16 15:36, Catalin Marinas wrote: >> On Mon, Feb 01, 2016 at 01:34:16PM +0000, Marc Zyngier wrote: >>> On 01/02/16 13:16, Christoffer Dall wrote: >>>> On Mon, Jan 25, 2016 at 03:53:40PM +0000, Marc Zyngier wrote: >>>>> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S >>>>> index 93e8d983..9e0683f 100644 >>>>> --- a/arch/arm64/kvm/hyp/hyp-entry.S >>>>> +++ b/arch/arm64/kvm/hyp/hyp-entry.S >>>>> @@ -38,6 +38,32 @@ >>>>> ldp x0, x1, [sp], #16 >>>>> .endm >>>>> >>>>> +.macro do_el2_call >>>>> + /* >>>>> + * Shuffle the parameters before calling the function >>>>> + * pointed to in x0. Assumes parameters in x[1,2,3]. >>>>> + */ >>>>> + stp lr, xzr, [sp, #-16]! >>>> >>>> remind me why this pair isn't just doing "str" instead of "stp" with the >>>> xzr ? >>> >>> Because SP has to be aligned on a 16 bytes boundary at all times. >> >> You could do something like: >> >> sub sp, sp, #16 >> str lr, [sp] >> > > Ah, fair enough. I'll fold that in. > Since we're micro-reviewing: what's wrong with str lr, [sp, #-16]! ? -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 01/02/16 17:08, Ard Biesheuvel wrote: > On 1 February 2016 at 17:20, Marc Zyngier <marc.zyngier@arm.com> wrote: >> On 01/02/16 15:36, Catalin Marinas wrote: >>> On Mon, Feb 01, 2016 at 01:34:16PM +0000, Marc Zyngier wrote: >>>> On 01/02/16 13:16, Christoffer Dall wrote: >>>>> On Mon, Jan 25, 2016 at 03:53:40PM +0000, Marc Zyngier wrote: >>>>>> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S >>>>>> index 93e8d983..9e0683f 100644 >>>>>> --- a/arch/arm64/kvm/hyp/hyp-entry.S >>>>>> +++ b/arch/arm64/kvm/hyp/hyp-entry.S >>>>>> @@ -38,6 +38,32 @@ >>>>>> ldp x0, x1, [sp], #16 >>>>>> .endm >>>>>> >>>>>> +.macro do_el2_call >>>>>> + /* >>>>>> + * Shuffle the parameters before calling the function >>>>>> + * pointed to in x0. Assumes parameters in x[1,2,3]. >>>>>> + */ >>>>>> + stp lr, xzr, [sp, #-16]! >>>>> >>>>> remind me why this pair isn't just doing "str" instead of "stp" with the >>>>> xzr ? >>>> >>>> Because SP has to be aligned on a 16 bytes boundary at all times. >>> >>> You could do something like: >>> >>> sub sp, sp, #16 >>> str lr, [sp] >>> >> >> Ah, fair enough. I'll fold that in. >> > > Since we're micro-reviewing: what's wrong with > > str lr, [sp, #-16]! > > ? > I suspect that on most micro-architectures, a register writeback is going to be slower than doing the sub independently. I may be wrong, though. M.
On Mon, Feb 01, 2016 at 05:28:32PM +0000, Marc Zyngier wrote: > On 01/02/16 17:08, Ard Biesheuvel wrote: > > On 1 February 2016 at 17:20, Marc Zyngier <marc.zyngier@arm.com> wrote: > >> On 01/02/16 15:36, Catalin Marinas wrote: > >>> On Mon, Feb 01, 2016 at 01:34:16PM +0000, Marc Zyngier wrote: > >>>> On 01/02/16 13:16, Christoffer Dall wrote: > >>>>> On Mon, Jan 25, 2016 at 03:53:40PM +0000, Marc Zyngier wrote: > >>>>>> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S > >>>>>> index 93e8d983..9e0683f 100644 > >>>>>> --- a/arch/arm64/kvm/hyp/hyp-entry.S > >>>>>> +++ b/arch/arm64/kvm/hyp/hyp-entry.S > >>>>>> @@ -38,6 +38,32 @@ > >>>>>> ldp x0, x1, [sp], #16 > >>>>>> .endm > >>>>>> > >>>>>> +.macro do_el2_call > >>>>>> + /* > >>>>>> + * Shuffle the parameters before calling the function > >>>>>> + * pointed to in x0. Assumes parameters in x[1,2,3]. > >>>>>> + */ > >>>>>> + stp lr, xzr, [sp, #-16]! > >>>>> > >>>>> remind me why this pair isn't just doing "str" instead of "stp" with the > >>>>> xzr ? > >>>> > >>>> Because SP has to be aligned on a 16 bytes boundary at all times. > >>> > >>> You could do something like: > >>> > >>> sub sp, sp, #16 > >>> str lr, [sp] > >>> > >> > >> Ah, fair enough. I'll fold that in. > >> > > > > Since we're micro-reviewing: what's wrong with > > > > str lr, [sp, #-16]! > > > > ? > > > > I suspect that on most micro-architectures, a register writeback is > going to be slower than doing the sub independently. > > I may be wrong, though. > For the record, I don't mind it the way it was in the original patch either, I was just curious about the store of xzr and had forgottten the stack alignment thing. -Christoffer -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S index 0ccdcbb..0689a74 100644 --- a/arch/arm64/kvm/hyp.S +++ b/arch/arm64/kvm/hyp.S @@ -17,7 +17,9 @@ #include <linux/linkage.h> +#include <asm/alternative.h> #include <asm/assembler.h> +#include <asm/cpufeature.h> /* * u64 kvm_call_hyp(void *hypfn, ...); @@ -38,6 +40,11 @@ * arch/arm64/kernel/hyp_stub.S. */ ENTRY(kvm_call_hyp) +alternative_if_not ARM64_HAS_VIRT_HOST_EXTN hvc #0 ret +alternative_else + b __vhe_hyp_call + nop +alternative_endif ENDPROC(kvm_call_hyp) diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S index 93e8d983..9e0683f 100644 --- a/arch/arm64/kvm/hyp/hyp-entry.S +++ b/arch/arm64/kvm/hyp/hyp-entry.S @@ -38,6 +38,32 @@ ldp x0, x1, [sp], #16 .endm +.macro do_el2_call + /* + * Shuffle the parameters before calling the function + * pointed to in x0. Assumes parameters in x[1,2,3]. + */ + stp lr, xzr, [sp, #-16]! + mov lr, x0 + mov x0, x1 + mov x1, x2 + mov x2, x3 + blr lr + ldp lr, xzr, [sp], #16 +.endm + +ENTRY(__vhe_hyp_call) + do_el2_call + /* + * We used to rely on having an exception return to get + * an implicit isb. In the E2H case, we don't have it anymore. + * rather than changing all the leaf functions, just do it here + * before returning to the rest of the kernel. + */ + isb + ret +ENDPROC(__vhe_hyp_call) + el1_sync: // Guest trapped into EL2 save_x0_to_x3 @@ -58,19 +84,13 @@ el1_sync: // Guest trapped into EL2 mrs x0, vbar_el2 b 2f -1: stp lr, xzr, [sp, #-16]! - +1: /* - * Compute the function address in EL2, and shuffle the parameters. + * Perform the EL2 call */ kern_hyp_va x0 - mov lr, x0 - mov x0, x1 - mov x1, x2 - mov x2, x3 - blr lr + do_el2_call - ldp lr, xzr, [sp], #16 2: eret el1_trap:
With VHE, the host never issues an HVC instruction to get into the KVM code, as we can simply branch there. Use runtime code patching to simplify things a bit. Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> --- arch/arm64/kvm/hyp.S | 7 +++++++ arch/arm64/kvm/hyp/hyp-entry.S | 38 +++++++++++++++++++++++++++++--------- 2 files changed, 36 insertions(+), 9 deletions(-)