linux-kernel - Re: [PATCH v3] selftests: KVM: avoid failures due to reserved HyperTransport region

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Date:   Tue, 14 Dec 2021 16:07:47 +0100
From:   Andrew Jones <drjones@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        seanjc@...gle.com, vkuznets@...hat.com, mlevitsk@...hat.com,
        joao.m.martins@...cle.com, stable@...r.kernel.org,
        David Matlack <dmatlack@...gle.com>
Subject: Re: [PATCH v3] selftests: KVM: avoid failures due to reserved
 HyperTransport region

On Thu, Dec 09, 2021 at 05:30:40PM -0500, Paolo Bonzini wrote:
> AMD proceessors define an address range that is reserved by HyperTransport
> and causes a failure if used for guest physical addresses.  Avoid
> selftests failures by reserving those guest physical addresses; the
> rules are:
> 
> - On parts with <40 bits, its fully hidden from software.
> 
> - Before Fam17h, it was always 12G just below 1T, even if there was more
> RAM above this location.  In this case we just not use any RAM above 1T.
> 
> - On Fam17h and later, it is variable based on SME, and is either just
> below 2^48 (no encryption) or 2^43 (encryption).
> 
> Fixes: ef4c9f4f6546 ("KVM: selftests: Fix 32-bit truncation of vm_get_max_gfn()")
> Cc: stable@...r.kernel.org
> Cc: David Matlack <dmatlack@...gle.com>
> Reported-by: Maxim Levitsky <mlevitsk@...hat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> Message-Id: <20210805105423.412878-1-pbonzini@...hat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  .../testing/selftests/kvm/include/kvm_util.h  |  9 +++
>  tools/testing/selftests/kvm/lib/kvm_util.c    |  2 +-
>  .../selftests/kvm/lib/x86_64/processor.c      | 69 +++++++++++++++++++
>  3 files changed, 79 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
> index 6a1a37f30494..da2b702da71a 100644
> --- a/tools/testing/selftests/kvm/include/kvm_util.h
> +++ b/tools/testing/selftests/kvm/include/kvm_util.h
> @@ -71,6 +71,15 @@ enum vm_guest_mode {
>  
>  #endif
>  
> +#if defined(__x86_64__)
> +unsigned long vm_compute_max_gfn(struct kvm_vm *vm);
> +#else
> +static inline unsigned long vm_compute_max_gfn(struct kvm_vm *vm)
> +{
> +	return ((1ULL << vm->pa_bits) >> vm->page_shift) - 1;
> +}

This breaks compiling on non-x86 architectures because of how we keep
the vm struct private. I'll send a patch that puts vm_compute_max_gfn
in lib/kvm_util.c but as a weak symbol.

(Maybe we should stop keeping the vm struct private...)

Thanks,
drew