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

[Sean Christopherson]

On Wed, Sep 13, 2023, isaku.yamahata@xxxxxxxxx wrote:
> From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> 
> Add config, HAVE_GENERIC_PRIVATE_MEM_HANDLE_ERROR, to indicate kvm arch
> can handle gmem error page.
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
> ---
>  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.