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

From: Sean Christopherson <seanjc@google.com>
To: isaku.yamahata@intel.com
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	 isaku.yamahata@gmail.com, Michael Roth <michael.roth@amd.com>,
	 Paolo Bonzini <pbonzini@redhat.com>,
	erdemaktas@google.com, Sagi Shahar <sagis@google.com>,
	 David Matlack <dmatlack@google.com>,
	Kai Huang <kai.huang@intel.com>,
	 Zhi Wang <zhi.wang.linux@gmail.com>,
	chen.bo@intel.com, linux-coco@lists.linux.dev,
	 Chao Peng <chao.p.peng@linux.intel.com>,
	Ackerley Tng <ackerleytng@google.com>,
	 Vishal Annapurve <vannapurve@google.com>,
	Yuan Yao <yuan.yao@linux.intel.com>,
	 Jarkko Sakkinen <jarkko@kernel.org>,
	Xu Yilun <yilun.xu@intel.com>,
	 Quentin Perret <qperret@google.com>,
	wei.w.wang@intel.com, Fuad Tabba <tabba@google.com>
Subject: Re: [RFC PATCH 1/6] KVM: guest_memfd: Add config to show the capability to handle error page
Date: Wed, 13 Sep 2023 09:16:11 -0700	[thread overview]
Message-ID: <ZQHgS13+QBChjYNw@google.com> (raw)
In-Reply-To: <56cd2f6f42351f2f27a07e5764bab7f689cc0059.1694599703.git.isaku.yamahata@intel.com>

On Wed, Sep 13, 2023, isaku.yamahata@intel.com wrote:
> From: Isaku Yamahata <isaku.yamahata@intel.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@intel.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.