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From: Oliver Upton <oliver.upton@linux.dev>
To: Ricardo Koller <ricarkol@google.com>
Cc: ricarkol@gmail.com, kvm@vger.kernel.org, catalin.marinas@arm.com,
	kvmarm@lists.linux.dev, andrew.jones@linux.dev,
	bgardon@google.com, maz@kernel.org, dmatlack@google.com,
	pbonzini@redhat.com, kvmarm@lists.cs.columbia.edu
Subject: Re: [RFC PATCH 01/12] KVM: arm64: Relax WARN check in stage2_make_pte()
Date: Mon, 14 Nov 2022 20:59:13 +0000	[thread overview]
Message-ID: <Y3KsIUpKISgYRAV9@google.com> (raw)
In-Reply-To: <20221112081714.2169495-2-ricarkol@google.com>

Hi Ricardo,

On Sat, Nov 12, 2022 at 08:17:03AM +0000, Ricardo Koller wrote:
> stage2_make_pte() throws a warning when used in a non-shared walk, as PTEs
> are not "locked" when walking non-shared. Add a check so it can be used
> non-shared.
> 
> Signed-off-by: Ricardo Koller <ricarkol@google.com>

I would very much prefer to leave this WARN as-is. Correct me if I am
wrong, but I do not believe this warning is firing with the existing
code.

While the locking portion doesn't make a whole lot of sense for a
non-shared walk, it is also a magic value that indicates we've already
done the break side of break-before-make. If the warning fires then that
would suggest our break-before-make implementation isn't working as
expected.

--
Thanks,
Oliver

> ---
>  arch/arm64/kvm/hyp/pgtable.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index c12462439e70..b16107bf917c 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -733,7 +733,8 @@ static void stage2_make_pte(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_t n
>  {
>  	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
>  
> -	WARN_ON(!stage2_pte_is_locked(*ctx->ptep));
> +	if (kvm_pgtable_walk_shared(ctx))
> +		WARN_ON(!stage2_pte_is_locked(*ctx->ptep));
>  
>  	if (stage2_pte_is_counted(new))
>  		mm_ops->get_page(ctx->ptep);
> -- 
> 2.38.1.431.g37b22c650d-goog
> 
> 
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WARNING: multiple messages have this Message-ID (diff)
From: Oliver Upton <oliver.upton@linux.dev>
To: Ricardo Koller <ricarkol@google.com>
Cc: pbonzini@redhat.com, maz@kernel.org, dmatlack@google.com,
	qperret@google.com, catalin.marinas@arm.com,
	andrew.jones@linux.dev, seanjc@google.com,
	alexandru.elisei@arm.com, suzuki.poulose@arm.com,
	eric.auger@redhat.com, gshan@redhat.com, reijiw@google.com,
	rananta@google.com, bgardon@google.com, kvm@vger.kernel.org,
	kvmarm@lists.linux.dev, kvmarm@lists.cs.columbia.edu,
	ricarkol@gmail.com
Subject: Re: [RFC PATCH 01/12] KVM: arm64: Relax WARN check in stage2_make_pte()
Date: Mon, 14 Nov 2022 20:59:13 +0000	[thread overview]
Message-ID: <Y3KsIUpKISgYRAV9@google.com> (raw)
Message-ID: <20221114205913.xD1o5G7ixh4xKXow8rGJHKWNLu56vx_eTtJLqU1V5gA@z> (raw)
In-Reply-To: <20221112081714.2169495-2-ricarkol@google.com>

Hi Ricardo,

On Sat, Nov 12, 2022 at 08:17:03AM +0000, Ricardo Koller wrote:
> stage2_make_pte() throws a warning when used in a non-shared walk, as PTEs
> are not "locked" when walking non-shared. Add a check so it can be used
> non-shared.
> 
> Signed-off-by: Ricardo Koller <ricarkol@google.com>

I would very much prefer to leave this WARN as-is. Correct me if I am
wrong, but I do not believe this warning is firing with the existing
code.

While the locking portion doesn't make a whole lot of sense for a
non-shared walk, it is also a magic value that indicates we've already
done the break side of break-before-make. If the warning fires then that
would suggest our break-before-make implementation isn't working as
expected.

--
Thanks,
Oliver

> ---
>  arch/arm64/kvm/hyp/pgtable.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index c12462439e70..b16107bf917c 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -733,7 +733,8 @@ static void stage2_make_pte(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_t n
>  {
>  	struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops;
>  
> -	WARN_ON(!stage2_pte_is_locked(*ctx->ptep));
> +	if (kvm_pgtable_walk_shared(ctx))
> +		WARN_ON(!stage2_pte_is_locked(*ctx->ptep));
>  
>  	if (stage2_pte_is_counted(new))
>  		mm_ops->get_page(ctx->ptep);
> -- 
> 2.38.1.431.g37b22c650d-goog
> 
> 

  reply	other threads:[~2022-11-14 20:59 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-12  8:17 [RFC PATCH 00/12] KVM: arm64: Eager huge-page splitting for dirty-logging Ricardo Koller
2022-11-12  8:17 ` Ricardo Koller
2022-11-12  8:17 ` [RFC PATCH 01/12] KVM: arm64: Relax WARN check in stage2_make_pte() Ricardo Koller
2022-11-12  8:17   ` Ricardo Koller
2022-11-14 20:59   ` Oliver Upton [this message]
2022-11-14 20:59     ` Oliver Upton
2022-11-12  8:17 ` [RFC PATCH 02/12] KVM: arm64: Allow visiting block PTEs in post-order Ricardo Koller
2022-11-12  8:17   ` Ricardo Koller
2022-11-14 18:48   ` Oliver Upton
2022-11-14 18:48     ` Oliver Upton
2023-01-13  3:44     ` Ricardo Koller
2022-11-12  8:17 ` [RFC PATCH 03/12] KVM: arm64: Add stage2_create_removed() Ricardo Koller
2022-11-12  8:17   ` Ricardo Koller
2022-11-12  8:17 ` [RFC PATCH 04/12] KVM: arm64: Add kvm_pgtable_stage2_split() Ricardo Koller
2022-11-12  8:17   ` Ricardo Koller
2022-11-14 20:54   ` Oliver Upton
2022-11-14 20:54     ` Oliver Upton
2022-11-15 23:03     ` Ricardo Koller
2022-11-15 23:03       ` Ricardo Koller
2022-11-15 23:27       ` Ricardo Koller
2022-11-15 23:27         ` Ricardo Koller
2022-11-15 23:54         ` Oliver Upton
2022-11-15 23:54           ` Oliver Upton
2022-11-17 21:50           ` Ricardo Koller
2022-11-17 21:50             ` Ricardo Koller
2022-11-12  8:17 ` [RFC PATCH 05/12] arm64: Add a capability for FEAT_BBM level 2 Ricardo Koller
2022-11-12  8:17   ` Ricardo Koller
2022-11-12  8:17 ` [RFC PATCH 06/12] KVM: arm64: Split block PTEs without using break-before-make Ricardo Koller
2022-11-12  8:17   ` Ricardo Koller
2022-11-14 18:56   ` Oliver Upton
2022-11-14 18:56     ` Oliver Upton
2022-11-12  8:17 ` [RFC PATCH 07/12] KVM: arm64: Refactor kvm_arch_commit_memory_region() Ricardo Koller
2022-11-12  8:17   ` Ricardo Koller
2022-11-12  8:17 ` [RFC PATCH 08/12] KVM: arm64: Add kvm_uninit_stage2_mmu() Ricardo Koller
2022-11-12  8:17   ` Ricardo Koller
2022-11-12  8:17 ` [RFC PATCH 09/12] KVM: arm64: Split huge pages when dirty logging is enabled Ricardo Koller
2022-11-12  8:17   ` Ricardo Koller
2022-11-12  8:17 ` [RFC PATCH 10/12] KVM: arm64: Open-code kvm_mmu_write_protect_pt_masked() Ricardo Koller
2022-11-12  8:17   ` Ricardo Koller
2022-11-12  8:17 ` [RFC PATCH 11/12] KVM: arm64: Split huge pages during KVM_CLEAR_DIRTY_LOG Ricardo Koller
2022-11-12  8:17   ` Ricardo Koller
2022-11-12  8:17 ` [RFC PATCH 12/12] KVM: arm64: Use local TLBI on permission relaxation Ricardo Koller
2022-11-12  8:17   ` Ricardo Koller
2022-11-14 18:42 ` [RFC PATCH 00/12] KVM: arm64: Eager huge-page splitting for dirty-logging Oliver Upton
2022-11-14 18:42   ` Oliver Upton
2023-01-13  3:42   ` Ricardo Koller

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