linux-kernel - Re: [PATCH v6 32/38] KVM: arm64: Introduce KVM_PGTABLE_S2

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Date:   Mon, 22 Mar 2021 12:19:34 +0000
From:   Will Deacon <will@...nel.org>
To:     Quentin Perret <qperret@...gle.com>
Cc:     catalin.marinas@....com, maz@...nel.org, james.morse@....com,
        julien.thierry.kdev@...il.com, suzuki.poulose@....com,
        android-kvm@...gle.com, seanjc@...gle.com, mate.toth-pal@....com,
        linux-kernel@...r.kernel.org, robh+dt@...nel.org,
        linux-arm-kernel@...ts.infradead.org, kernel-team@...roid.com,
        kvmarm@...ts.cs.columbia.edu, tabba@...gle.com, ardb@...nel.org,
        mark.rutland@....com, dbrazdil@...gle.com
Subject: Re: [PATCH v6 32/38] KVM: arm64: Introduce KVM_PGTABLE_S2_NOFWB
 stage 2 flag

On Fri, Mar 19, 2021 at 10:01:40AM +0000, Quentin Perret wrote:
> In order to further configure stage 2 page-tables, pass flags to the
> init function using a new enum.
> 
> The first of these flags allows to disable FWB even if the hardware
> supports it as we will need to do so for the host stage 2.
> 
> Signed-off-by: Quentin Perret <qperret@...gle.com>
> ---
>  arch/arm64/include/asm/kvm_pgtable.h  | 43 +++++++++++++-------
>  arch/arm64/include/asm/pgtable-prot.h |  4 +-
>  arch/arm64/kvm/hyp/pgtable.c          | 56 +++++++++++++++------------
>  3 files changed, 62 insertions(+), 41 deletions(-)

[...]

> diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
> index 9a65fb528110..079f4e9a3e84 100644
> --- a/arch/arm64/include/asm/pgtable-prot.h
> +++ b/arch/arm64/include/asm/pgtable-prot.h
> @@ -71,10 +71,10 @@ extern bool arm64_use_ng_mappings;
>  #define PAGE_KERNEL_EXEC	__pgprot(PROT_NORMAL & ~PTE_PXN)
>  #define PAGE_KERNEL_EXEC_CONT	__pgprot((PROT_NORMAL & ~PTE_PXN) | PTE_CONT)
>  
> -#define PAGE_S2_MEMATTR(attr)						\
> +#define PAGE_S2_MEMATTR(attr, has_fwb)					\
>  	({								\
>  		u64 __val;						\
> -		if (cpus_have_const_cap(ARM64_HAS_STAGE2_FWB))		\
> +		if (has_fwb)						\
>  			__val = PTE_S2_MEMATTR(MT_S2_FWB_ ## attr);	\
>  		else							\
>  			__val = PTE_S2_MEMATTR(MT_S2_ ## attr);		\

Given that this isn't used outside of pgtable.c, I wonder if we should move
it in there, as it's a pretty low-level thing to do now that it takes the
'has_fwb' parameter.

But regardless,

Acked-by: Will Deacon <will@...nel.org>

Will