linux-kernel - Re: [RFC PATCH 1/6] KVM: guest_memfd: Add config to show the capability to handle error page

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Date:   Wed, 13 Sep 2023 09:16:11 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     isaku.yamahata@...el.com
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        isaku.yamahata@...il.com, Michael Roth <michael.roth@....com>,
        Paolo Bonzini <pbonzini@...hat.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>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Xu Yilun <yilun.xu@...el.com>,
        Quentin Perret <qperret@...gle.com>, wei.w.wang@...el.com,
        Fuad Tabba <tabba@...gle.com>
Subject: Re: [RFC PATCH 1/6] KVM: guest_memfd: Add config to show the
 capability to handle error page

On Wed, Sep 13, 2023, isaku.yamahata@...el.com wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
> 
> Add config, HAVE_GENERIC_PRIVATE_MEM_HANDLE_ERROR, to indicate kvm arch
> can handle gmem error page.
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
>  virt/kvm/Kconfig     | 3 +++
>  virt/kvm/guest_mem.c | 3 +++
>  2 files changed, 6 insertions(+)
> 
> diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
> index 1a48cb530092..624df45baff0 100644
> --- a/virt/kvm/Kconfig
> +++ b/virt/kvm/Kconfig
> @@ -112,3 +112,6 @@ config KVM_GENERIC_PRIVATE_MEM
>         select KVM_GENERIC_MEMORY_ATTRIBUTES
>         select KVM_PRIVATE_MEM
>         bool
> +
> +config HAVE_GENERIC_PRIVATE_MEM_HANDLE_ERROR
> +	bool
> diff --git a/virt/kvm/guest_mem.c b/virt/kvm/guest_mem.c
> index 85903c32163f..35d8f03e7937 100644
> --- a/virt/kvm/guest_mem.c
> +++ b/virt/kvm/guest_mem.c
> @@ -307,6 +307,9 @@ static int kvm_gmem_error_page(struct address_space *mapping, struct page *page)
>  	pgoff_t start, end;
>  	gfn_t gfn;
>  
> +	if (!IS_ENABLED(CONFIG_HAVE_GENERIC_PRIVATE_MEM_HANDLE_ERROR))
> +		return MF_IGNORED;

I don't see the point, KVM can and should always zap SPTEs, i.e. can force the
geust to re-fault on the affected memory.  At that point kvm_gmem_get_pfn() will
return -EHWPOISON and architectures that don't support graceful recovery can
simply terminate the VM.