linux-kernel - Re: [PATCH 2/2] x86: sgx_vepc: implement SGX_IOC_VEPC

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Date:   Tue, 14 Sep 2021 22:55:08 +1200
From:   Kai Huang <kai.huang@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org, x86@...nel.org,
        linux-sgx@...r.kernel.org, jarkko@...nel.org,
        dave.hansen@...ux.intel.com, yang.zhong@...el.com
Subject: Re: [PATCH 2/2] x86: sgx_vepc: implement SGX_IOC_VEPC_REMOVE ioctl

On Mon, 13 Sep 2021 09:11:53 -0400 Paolo Bonzini wrote:
> Windows expects all pages to be in uninitialized state on startup.
> Add a ioctl that does this with EREMOVE, so that userspace can bring
> the pages back to this state also when resetting the VM.
> Pure userspace implementations, such as closing and reopening the device,
> are racy.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/include/uapi/asm/sgx.h |  2 ++
>  arch/x86/kernel/cpu/sgx/virt.c  | 36 +++++++++++++++++++++++++++++++++
>  2 files changed, 38 insertions(+)
> 
> diff --git a/arch/x86/include/uapi/asm/sgx.h b/arch/x86/include/uapi/asm/sgx.h
> index 9690d6899ad9..f79d84ce8033 100644
> --- a/arch/x86/include/uapi/asm/sgx.h
> +++ b/arch/x86/include/uapi/asm/sgx.h
> @@ -27,6 +27,8 @@ enum sgx_page_flags {
>  	_IOW(SGX_MAGIC, 0x02, struct sgx_enclave_init)
>  #define SGX_IOC_ENCLAVE_PROVISION \
>  	_IOW(SGX_MAGIC, 0x03, struct sgx_enclave_provision)
> +#define SGX_IOC_VEPC_REMOVE \
> +	_IO(SGX_MAGIC, 0x04)

Perhaps SGX_IOC_VEPC_RESET is better than REMOVE, since this ioctl doesn't
actually remove any EPC page from virtual EPC device, but just reset to a clean
slate (by using EREMOVE).