linux-kernel - Re: [PATCH 2/2] KVM: SVM: add some info prints to SEV init

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Message-ID: <CAEivzxd6GFMcW-k_dNKy83bHgPfa7iMivE=kdV-88Vkp28H2WA@mail.gmail.com>
Date:   Wed, 12 Apr 2023 16:55:58 +0200
From:   Aleksandr Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
To:     Zhi Wang <zhi.wang.linux@...il.com>
Cc:     pbonzini@...hat.com, Sean Christopherson <seanjc@...gle.com>,
        Stéphane Graber <stgraber@...ntu.com>,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] KVM: SVM: add some info prints to SEV init

On Tue, Apr 11, 2023 at 9:43 PM Zhi Wang <zhi.wang.linux@...il.com> wrote:
>
> On Tue,  4 Apr 2023 14:26:52 +0200
> Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com> wrote:
>
> > Let's add a few pr_info's to sev_hardware_setup to make SEV/SEV-ES
> > enabling a little bit handier for users. Right now it's too hard
> > to guess why SEV/SEV-ES are failing to enable.
> >
> > There are a few reasons.
> > SEV:
> > - npt is disabled (module parameter)
>      ^NPT
> > - CPU lacks some features (sev, decodeassists)
> > - Maximum SEV ASID is 0
> >
> > SEV-ES:
> > - mmio_caching is disabled (module parameter)
> > - CPU lacks sev_es feature
> > - Minimum SEV ASID value is 1 (can be adjusted in BIOS/UEFI)
> >
> > Cc: Sean Christopherson <seanjc@...gle.com>
> > Cc: Paolo Bonzini <pbonzini@...hat.com>
> > Cc: Stéphane Graber <stgraber@...ntu.com>
> > Cc: kvm@...r.kernel.org
> > Cc: linux-kernel@...r.kernel.org
> > Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
> > ---
> >  arch/x86/kvm/svm/sev.c | 27 +++++++++++++++++++++------
> >  1 file changed, 21 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> > index a42536a0681a..14cbb8f14c6b 100644
> > --- a/arch/x86/kvm/svm/sev.c
> > +++ b/arch/x86/kvm/svm/sev.c
> > @@ -2168,17 +2168,24 @@ void __init sev_hardware_setup(void)
> >       bool sev_es_supported = false;
> >       bool sev_supported = false;
> >
> > -     if (!sev_enabled || !npt_enabled)
> > +     if (!sev_enabled)
> >               goto out;
> >
> > +     if (!npt_enabled) {
> > +             pr_info("Failed to enable AMD SEV as it requires Nested Paging to be enabled\n");
> > +             goto out;
>
> Shouldn't we use pr_err() for error message?

I'm not sure. Because technically that's not an error, that is an
information message about current configuration.


>
> > +     }
> > +
> >       /*
> >        * SEV must obviously be supported in hardware.  Sanity check that the
> >        * CPU supports decode assists, which is mandatory for SEV guests to
> >        * support instruction emulation.
> >        */
> >       if (!boot_cpu_has(X86_FEATURE_SEV) ||
> > -         WARN_ON_ONCE(!boot_cpu_has(X86_FEATURE_DECODEASSISTS)))
> > +         WARN_ON_ONCE(!boot_cpu_has(X86_FEATURE_DECODEASSISTS))) {
> > +             pr_info("Failed to enable AMD SEV as it requires decodeassists and sev CPU features\n");
> >               goto out;
> > +     }
> >
> >       /* Retrieve SEV CPUID information */
> >       cpuid(0x8000001f, &eax, &ebx, &ecx, &edx);
> > @@ -2188,8 +2195,10 @@ void __init sev_hardware_setup(void)
> >
> >       /* Maximum number of encrypted guests supported simultaneously */
> >       max_sev_asid = ecx;
> > -     if (!max_sev_asid)
> > +     if (!max_sev_asid) {
> > +             pr_info("Failed to enable SEV as the maximum SEV ASID value is 0.\n");
> >               goto out;
> > +     }
> >
> >       /* Minimum ASID value that should be used for SEV guest */
> >       min_sev_asid = edx;
> > @@ -2234,16 +2243,22 @@ void __init sev_hardware_setup(void)
> >        * instead relies on #NPF(RSVD) being reflected into the guest as #VC
> >        * (the guest can then do a #VMGEXIT to request MMIO emulation).
> >        */
> > -     if (!enable_mmio_caching)
> > +     if (!enable_mmio_caching) {
> > +             pr_info("Failed to enable SEV-ES as it requires MMIO caching to be enabled\n");
> >               goto out;
> > +     }
> >
> >       /* Does the CPU support SEV-ES? */
> > -     if (!boot_cpu_has(X86_FEATURE_SEV_ES))
> > +     if (!boot_cpu_has(X86_FEATURE_SEV_ES)) {
> > +             pr_info("Failed to enable SEV-ES as it requires sev_es CPU feature\n");
> >               goto out;
> > +     }
> >
> >       /* Has the system been allocated ASIDs for SEV-ES? */
> > -     if (min_sev_asid == 1)
> > +     if (min_sev_asid == 1) {
> > +             pr_info("Failed to enable SEV-ES as the minimum SEV ASID value is 1.\n");
> >               goto out;
> > +     }
> >
> >       sev_es_asid_count = min_sev_asid - 1;
> >       if (misc_cg_set_capacity(MISC_CG_RES_SEV_ES, sev_es_asid_count))
>
> As this patch is making sev_hardware_setup()more informative, it would be
> better to print both ASID range and count (instead of only ASID count in
> the current code). I was suspecting there seems a bug of ASID range allocation
> in the current code, but I don't have the HW to test yet...