linux-kernel - Re: [RFC PATCH v6 006/104] KVM: TDX: Detect CPU feature on kernel module initialization

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Date:   Thu, 26 May 2022 12:28:44 -0700
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     Sagi Shahar <sagis@...gle.com>
Cc:     "Yamahata, Isaku" <isaku.yamahata@...el.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
        Paolo Bonzini <pbonzini@...hat.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH v6 006/104] KVM: TDX: Detect CPU feature on kernel
 module initialization

On Mon, May 23, 2022 at 04:47:59PM -0700,
Sagi Shahar <sagis@...gle.com> wrote:

> > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> > new file mode 100644
> > index 000000000000..9e26e3fa60ee
> > --- /dev/null
> > +++ b/arch/x86/kvm/vmx/tdx.c
> > @@ -0,0 +1,39 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +#include <linux/cpu.h>
> > +
> > +#include <asm/tdx.h>
> > +
> > +#include "capabilities.h"
> > +#include "x86_ops.h"
> > +
> > +#undef pr_fmt
> > +#define pr_fmt(fmt) "tdx: " fmt
> > +
> > +static u64 hkid_mask __ro_after_init;
> > +static u8 hkid_start_pos __ro_after_init;
> > +
> > +int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops)
> > +{
> > +       u32 max_pa;
> > +
> > +       if (!enable_ept) {
> > +               pr_warn("Cannot enable TDX with EPT disabled\n");
> > +               return -EINVAL;
> > +       }
> > +
> > +       if (!platform_has_tdx()) {
> > +               if (__seamrr_enabled())
> > +                       pr_warn("Cannot enable TDX with SEAMRR disabled\n");
> 
> So if we fail for another reason (e.g. tdx_keyid_sufficient returns
> false) we are going to fail silently and disable TDX without any log
> saying what happened. This will make it difficult to debug TDX
> initialization issues.

Agreed.  I've updated it as follows.

+int __init tdx_hardware_setup(struct kvm_x86_ops *x86_ops)
+{
+       u32 max_pa;
+
+       if (!enable_ept) {
+               pr_warn("Cannot enable TDX with EPT disabled\n");
+               return -EINVAL;
+       }
+
+       if (!platform_has_tdx()) {
+               if (__seamrr_enabled())
+                       pr_warn("Cannot enable TDX with SEAMRR disabled\n");
+               else
+                       pr_warn("Cannot enable TDX on TDX disabled platform.\n");
+               return -ENODEV;
+       }
+
+       /* Safe guard check because TDX overrides tlb_remote_flush callback. */
+       if (WARN_ON_ONCE(x86_ops->tlb_remote_flush))
+               return -EIO;
+
+       max_pa = cpuid_eax(0x80000008) & 0xff;
+       hkid_start_pos = boot_cpu_data.x86_phys_bits;
+       hkid_mask = GENMASK_ULL(max_pa - 1, hkid_start_pos);
+       pr_info("kvm: TDX is supported. hkid start pos %d mask 0x%llx\n",
+               hkid_start_pos, hkid_mask);
+
+       return 0;
+}
-- 
Isaku Yamahata <isaku.yamahata@...il.com>