Re: [RFC PATCH 1/8] KVM: arm64: Factor out firmware register handling from psci.c

[Oliver Upton <oupton@google.com>]

On Thu, Nov 04, 2021 at 10:16:21AM -0700, Raghavendra Rao Ananta wrote:
> Hi Oliver,
> 
> On Wed, Nov 3, 2021 at 2:43 PM Oliver Upton <oupton@google.com> wrote:
> >
> > Hi Raghu,
> >
> > On Tue, Nov 02, 2021 at 12:21:56AM +0000, Raghavendra Rao Ananta wrote:
> > > Common hypercall firmware register handing is currently employed
> > > by psci.c. Since the upcoming patches add more of these registers,
> > > it's better to move the generic handling to hypercall.c for a
> > > cleaner presentation.
> > >
> > > While we are at it, collect all the firmware registers under
> > > fw_reg_ids[] to help implement kvm_arm_get_fw_num_regs() and
> > > kvm_arm_copy_fw_reg_indices() in a generic way.
> > >
> > > No functional change intended.
> > >
> > > Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
> > > ---
> > >  arch/arm64/kvm/guest.c       |   2 +-
> > >  arch/arm64/kvm/hypercalls.c  | 151 +++++++++++++++++++++++++++++++
> > >  arch/arm64/kvm/psci.c        | 167 +++--------------------------------
> > >  include/kvm/arm_hypercalls.h |   7 ++
> > >  include/kvm/arm_psci.h       |   8 +-
> > >  5 files changed, 172 insertions(+), 163 deletions(-)
> > >
> > > diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> > > index 5ce26bedf23c..625f97f7b304 100644
> > > --- a/arch/arm64/kvm/guest.c
> > > +++ b/arch/arm64/kvm/guest.c
> > > @@ -18,7 +18,7 @@
> > >  #include <linux/string.h>
> > >  #include <linux/vmalloc.h>
> > >  #include <linux/fs.h>
> > > -#include <kvm/arm_psci.h>
> > > +#include <kvm/arm_hypercalls.h>
> > >  #include <asm/cputype.h>
> > >  #include <linux/uaccess.h>
> > >  #include <asm/fpsimd.h>
> > > diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
> > > index 30da78f72b3b..d030939c5929 100644
> > > --- a/arch/arm64/kvm/hypercalls.c
> > > +++ b/arch/arm64/kvm/hypercalls.c
> > > @@ -146,3 +146,154 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
> > >       smccc_set_retval(vcpu, val[0], val[1], val[2], val[3]);
> > >       return 1;
> > >  }
> > > +
> > > +static const u64 fw_reg_ids[] = {
> > > +     KVM_REG_ARM_PSCI_VERSION,
> > > +     KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1,
> > > +     KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2,
> > > +};
> > > +
> > > +int kvm_arm_get_fw_num_regs(struct kvm_vcpu *vcpu)
> > > +{
> > > +     return ARRAY_SIZE(fw_reg_ids);
> > > +}
> > > +
> > > +int kvm_arm_copy_fw_reg_indices(struct kvm_vcpu *vcpu, u64 __user *uindices)
> > > +{
> > > +     int i;
> > > +
> > > +     for (i = 0; i < ARRAY_SIZE(fw_reg_ids); i++) {
> > > +             if (put_user(fw_reg_ids[i], uindices))
> > > +                     return -EFAULT;
> > > +     }
> > > +
> > > +     return 0;
> > > +}
> >
> > It would appear that this patch is separating out the hypercall services
> > to each handle their own FW regs. At the same time, this is
> > consolidating the register enumeration into a single place.
> >
> > It would be nice to keep the scoping consistent with your accessors
> > below, or simply just handle all regs in hypercalls.c. Abstracting
> > per-service might result in a lot of boilerplate, though.
> >
> It's neither here nor there, unfortunately, because of how the fw
> registers exists. We have a dedicated fw register for psci and a file
> of its own (psci.c). Some of the other services, such as TRNG, have
> their own file, but because of the bitmap design, they won't have
> their own fw register. And the ARCH_WORKAROUND have their dedicated
> registers, but no file of their own. So, at best I was aiming to push
> all the things relevant to a service in its own file (psci for
> example), just to have a better file-context, while leaving others
> (and generic handling stuff) in hypercall.c.
> 
> Just to maintain consistency, I can create a dedicated file for the
> ARCH_WORKAROUND registers, if you feel that's better.
>

Perhaps the easiest thing to do would be to keep all firmware ID
registers in one place, much like we do for the ARM feature ID regs in
sys_regs.c.

> > > +#define KVM_REG_FEATURE_LEVEL_WIDTH  4
> > > +#define KVM_REG_FEATURE_LEVEL_MASK   (BIT(KVM_REG_FEATURE_LEVEL_WIDTH) - 1)
> > > +
> > > +/*
> > > + * Convert the workaround level into an easy-to-compare number, where higher
> > > + * values mean better protection.
> > > + */
> > > +static int get_kernel_wa_level(u64 regid)
> > > +{
> > > +     switch (regid) {
> > > +     case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1:
> > > +             switch (arm64_get_spectre_v2_state()) {
> > > +             case SPECTRE_VULNERABLE:
> > > +                     return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_AVAIL;
> > > +             case SPECTRE_MITIGATED:
> > > +                     return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_AVAIL;
> > > +             case SPECTRE_UNAFFECTED:
> > > +                     return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_REQUIRED;
> > > +             }
> > > +             return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_AVAIL;
> > > +     case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2:
> > > +             switch (arm64_get_spectre_v4_state()) {
> > > +             case SPECTRE_MITIGATED:
> > > +                     /*
> > > +                      * As for the hypercall discovery, we pretend we
> > > +                      * don't have any FW mitigation if SSBS is there at
> > > +                      * all times.
> > > +                      */
> > > +                     if (cpus_have_final_cap(ARM64_SSBS))
> > > +                             return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_AVAIL;
> > > +                     fallthrough;
> > > +             case SPECTRE_UNAFFECTED:
> > > +                     return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_REQUIRED;
> > > +             case SPECTRE_VULNERABLE:
> > > +                     return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_AVAIL;
> > > +             }
> > > +     }
> > > +
> > > +     return -EINVAL;
> > > +}
> > > +
> > > +int kvm_arm_get_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
> > > +{
> > > +     void __user *uaddr = (void __user *)(long)reg->addr;
> > > +     u64 val;
> > > +
> > > +     switch (reg->id) {
> > > +     case KVM_REG_ARM_PSCI_VERSION:
> > > +             val = kvm_psci_version(vcpu, vcpu->kvm);
> >
> > Should this become kvm_arm_get_fw_reg() to consistently genericize the
> > PSCI FW register accessors?
> >
> Sorry, I didn't follow. Did you mean, "kvm_arm_get_psci_fw_reg()"?

Right :) Of course, this could become irrelevant depending on how you
address scoping of the FW regs.

--
Thanks,
Oliver
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