linux-kernel - Re: [PATCH 4/8] KVM: gmem: protect kvm_mmu_invalidate

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Message-Id: <CUU93XA8UKMG.X15YWDK533GB@suppilovahvero>
Date:   Wed, 16 Aug 2023 23:28:15 +0300
From:   "Jarkko Sakkinen" <jarkko@...nel.org>
To:     <isaku.yamahata@...el.com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Cc:     <isaku.yamahata@...il.com>, "Michael Roth" <michael.roth@....com>,
        "Paolo Bonzini" <pbonzini@...hat.com>,
        "Sean Christopherson" <seanjc@...gle.com>, <erdemaktas@...gle.com>,
        "Sagi Shahar" <sagis@...gle.com>,
        "David Matlack" <dmatlack@...gle.com>,
        "Kai Huang" <kai.huang@...el.com>,
        "Zhi Wang" <zhi.wang.linux@...il.com>, <chen.bo@...el.com>,
        <linux-coco@...ts.linux.dev>,
        "Chao Peng" <chao.p.peng@...ux.intel.com>,
        "Ackerley Tng" <ackerleytng@...gle.com>,
        "Vishal Annapurve" <vannapurve@...gle.com>,
        "Yuan Yao" <yuan.yao@...ux.intel.com>,
        "Xu Yilun" <yilun.xu@...el.com>,
        "Quentin Perret" <qperret@...gle.com>, <wei.w.wang@...el.com>,
        "Fuad Tabba" <tabba@...gle.com>
Subject: Re: [PATCH 4/8] KVM: gmem: protect kvm_mmu_invalidate_end()

On Tue Aug 15, 2023 at 8:18 PM EEST,  wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
>
> kvm_mmu_invalidate_end() updates struct kvm::mmu_invalidate_in_progress
> and it's protected by kvm::mmu_lock.  call kvm_mmu_invalidate_end() before
> unlocking it. Not after the unlock.
>
> Fixes: 8e9009ca6d14 ("KVM: Introduce per-page memory attributes")
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
>  virt/kvm/kvm_main.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 8bfeb615fc4d..49380cd62367 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -535,6 +535,7 @@ struct kvm_mmu_notifier_range {
>  	} arg;
>  	gfn_handler_t handler;
>  	on_lock_fn_t on_lock;
> +	on_unlock_fn_t before_unlock;
>  	on_unlock_fn_t on_unlock;
>  	bool flush_on_ret;
>  	bool may_block;
> @@ -629,6 +630,8 @@ static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
>  		kvm_flush_remote_tlbs(kvm);
>  
>  	if (locked) {
> +		if (!IS_KVM_NULL_FN(range->before_unlock))
> +			range->before_unlock(kvm);
>  		KVM_MMU_UNLOCK(kvm);
>  		if (!IS_KVM_NULL_FN(range->on_unlock))
>  			range->on_unlock(kvm);
> @@ -653,6 +656,7 @@ static __always_inline int kvm_handle_hva_range(struct mmu_notifier *mn,
>  		.arg.pte	= pte,
>  		.handler	= handler,
>  		.on_lock	= (void *)kvm_null_fn,
> +		.before_unlock	= (void *)kvm_null_fn,
>  		.on_unlock	= (void *)kvm_null_fn,
>  		.flush_on_ret	= true,
>  		.may_block	= false,
> @@ -672,6 +676,7 @@ static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn
>  		.end		= end,
>  		.handler	= handler,
>  		.on_lock	= (void *)kvm_null_fn,
> +		.before_unlock	= (void *)kvm_null_fn,
>  		.on_unlock	= (void *)kvm_null_fn,
>  		.flush_on_ret	= false,
>  		.may_block	= false,
> @@ -776,6 +781,7 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
>  		.end		= range->end,
>  		.handler	= kvm_mmu_unmap_gfn_range,
>  		.on_lock	= kvm_mmu_invalidate_begin,
> +		.before_unlock	= (void *)kvm_null_fn,
>  		.on_unlock	= kvm_arch_guest_memory_reclaimed,
>  		.flush_on_ret	= true,
>  		.may_block	= mmu_notifier_range_blockable(range),
> @@ -815,6 +821,8 @@ static int kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
>  
>  void kvm_mmu_invalidate_end(struct kvm *kvm)
>  {
> +	lockdep_assert_held_write(&kvm->mmu_lock);
> +
>  	/*
>  	 * This sequence increase will notify the kvm page fault that
>  	 * the page that is going to be mapped in the spte could have
> @@ -846,6 +854,7 @@ static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
>  		.end		= range->end,
>  		.handler	= (void *)kvm_null_fn,
>  		.on_lock	= kvm_mmu_invalidate_end,
> +		.before_unlock	= (void *)kvm_null_fn,
>  		.on_unlock	= (void *)kvm_null_fn,
>  		.flush_on_ret	= false,
>  		.may_block	= mmu_notifier_range_blockable(range),
> @@ -2433,6 +2442,8 @@ static __always_inline void kvm_handle_gfn_range(struct kvm *kvm,
>  		kvm_flush_remote_tlbs(kvm);
>  
>  	if (locked) {
> +		if (!IS_KVM_NULL_FN(range->before_unlock))
> +			range->before_unlock(kvm);
>  		KVM_MMU_UNLOCK(kvm);
>  		if (!IS_KVM_NULL_FN(range->on_unlock))
>  			range->on_unlock(kvm);
> @@ -2447,6 +2458,7 @@ static int kvm_vm_set_mem_attributes(struct kvm *kvm, unsigned long attributes,
>  		.end = end,
>  		.handler = kvm_mmu_unmap_gfn_range,
>  		.on_lock = kvm_mmu_invalidate_begin,
> +		.before_unlock	= (void *)kvm_null_fn,
>  		.on_unlock = (void *)kvm_null_fn,
>  		.flush_on_ret = true,
>  		.may_block = true,
> @@ -2457,7 +2469,8 @@ static int kvm_vm_set_mem_attributes(struct kvm *kvm, unsigned long attributes,
>  		.arg.attributes = attributes,
>  		.handler = kvm_arch_post_set_memory_attributes,
>  		.on_lock = (void *)kvm_null_fn,
> -		.on_unlock = kvm_mmu_invalidate_end,
> +		.before_unlock = kvm_mmu_invalidate_end,
> +		.on_unlock = (void *)kvm_null_fn,
>  		.may_block = true,
>  	};
>  	unsigned long i;
> -- 
> 2.25.1

Acked-by: Jarkko Sakkinen <jarkko@...nel.org>

BR, Jarkko