Subject: Re: [PATCH 04/17] arm64: Provide an 'upgrade to VHE' stub hypercall

From: Marc Zyngier <[email-masked]>
Date: Tue, 05 Jan 2021 08:24:21 +0000

On 2021-01-04 23:39, Jing Zhang wrote:
> On Mon, Dec 28, 2020 at 4:50 AM Marc Zyngier <[email-masked]> wrote:
>> 
>> As we are about to change the way a VHE system boots, let's
>> provide the core helper, in the form of a stub hypercall that
>> enables VHE and replicates the full EL1 context at EL2, thanks
>> to EL1 and VHE-EL2 being extremely similar.
>> 
>> On exception return, the kernel carries on at EL2. Fancy!
>> 
>> Nothing calls this new hypercall yet, so no functional change.
>> 
>> Signed-off-by: Marc Zyngier <[email-masked]>
>> ---
>>  arch/arm64/include/asm/virt.h |  7 +++-
>>  arch/arm64/kernel/hyp-stub.S  | 70 
>> ++++++++++++++++++++++++++++++++++-
>>  2 files changed, 74 insertions(+), 3 deletions(-)
>> 
>> diff --git a/arch/arm64/include/asm/virt.h 
>> b/arch/arm64/include/asm/virt.h
>> index ee6a48df89d9..7379f35ae2c6 100644
>> --- a/arch/arm64/include/asm/virt.h
>> +++ b/arch/arm64/include/asm/virt.h
>> @@ -35,8 +35,13 @@
>>   */
>>  #define HVC_RESET_VECTORS 2
>> 
>> +/*
>> + * HVC_VHE_RESTART - Upgrade the CPU from EL1 to EL2, if possible
>> + */
>> +#define HVC_VHE_RESTART        3
>> +
>>  /* Max number of HYP stub hypercalls */
>> -#define HVC_STUB_HCALL_NR 3
>> +#define HVC_STUB_HCALL_NR 4
>> 
>>  /* Error returned when an invalid stub number is passed into x0 */
>>  #define HVC_STUB_ERR   0xbadca11
>> diff --git a/arch/arm64/kernel/hyp-stub.S 
>> b/arch/arm64/kernel/hyp-stub.S
>> index 160f5881a0b7..6ffdc1f7778b 100644
>> --- a/arch/arm64/kernel/hyp-stub.S
>> +++ b/arch/arm64/kernel/hyp-stub.S
>> @@ -8,9 +8,9 @@
>> 
>>  #include <linux/init.h>
>>  #include <linux/linkage.h>
>> -#include <linux/irqchip/arm-gic-v3.h>
>> 
>>  #include <asm/assembler.h>
>> +#include <asm/el2_setup.h>
>>  #include <asm/kvm_arm.h>
>>  #include <asm/kvm_asm.h>
>>  #include <asm/ptrace.h>
>> @@ -47,10 +47,16 @@ SYM_CODE_END(__hyp_stub_vectors)
>> 
>>  SYM_CODE_START_LOCAL(el1_sync)
>>         cmp     x0, #HVC_SET_VECTORS
>> -       b.ne    2f
>> +       b.ne    1f
>>         msr     vbar_el2, x1
>>         b       9f
>> 
>> +1:     cmp     x0, #HVC_VHE_RESTART
>> +       b.ne    2f
>> +       mov     x0, #HVC_SOFT_RESTART
>> +       adr     x1, mutate_to_vhe
>> +       // fall through...
>> +
>>  2:     cmp     x0, #HVC_SOFT_RESTART
>>         b.ne    3f
>>         mov     x0, x2
>> @@ -70,6 +76,66 @@ SYM_CODE_START_LOCAL(el1_sync)
>>         eret
>>  SYM_CODE_END(el1_sync)
>> 
>> +// nVHE? No way! Give me the real thing!
>> +SYM_CODE_START_LOCAL(mutate_to_vhe)
>> +       // Sanity check: MMU *must* be off
>> +       mrs     x0, sctlr_el2
>> +       tbnz    x0, #0, 1f
>> +
>> +       // Needs to be VHE capable, obviously
>> +       mrs     x0, id_aa64mmfr1_el1
>> +       ubfx    x0, x0, #ID_AA64MMFR1_VHE_SHIFT, #4
>> +       cbz     x0, 1f
>> +
>> +       // Engage the VHE magic!
>> +       mov_q   x0, HCR_HOST_VHE_FLAGS
>> +       msr     hcr_el2, x0
>> +       isb
>> +
>> +       // Doesn't do much on VHE, but still, worth a shot
>> +       init_el2_state vhe
>> +
>> +       // Use the EL1 allocated stack, per-cpu offset
>> +       mrs     x0, sp_el1
>> +       mov     sp, x0
>> +       mrs     x0, tpidr_el1
>> +       msr     tpidr_el2, x0
>> +
>> +       // FP configuration, vectors
>> +       mrs_s   x0, SYS_CPACR_EL12
>> +       msr     cpacr_el1, x0
>> +       mrs_s   x0, SYS_VBAR_EL12
>> +       msr     vbar_el1, x0
>> +
>> +       // Transfert the MM state from EL1 to EL2
> 
> Transfert, typo?

Yes, thanks.

If you are going to review this, may I suggest you look at v2 [1]
instead? The initial version had so many issues that I'm trying
to pretend it never happened.

Cheers,

         M.

[1] https://lore.kernel.org/r/[email-masked]
-- 
Jazz is not dead. It just smells funny...

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