linux-kernel - Question on get random long worse in VM than on host

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Message-ID: <214e37e9-7aba-1e61-f63f-85cb10c9a878@huawei.com>
Date: Sat, 31 Aug 2024 11:34:33 +0800
From: Tangnianyao <tangnianyao@...wei.com>
To: Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
	<oliver.upton@...ux.dev>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <kvmarm@...ts.linux.dev>
CC: "guoyang (C)" <guoyang2@...wei.com>
Subject: Question on get random long worse in VM than on host

Hi, all

On ARM64 server(Kunpeng), performance of some syscall cases (like fork

and open) in guest, which need random u64, are 10~20% worse than

those on host. Because CONFIG_ARCH_HAS_ELF_RANDOMIZE=y and

CONFIG_STACKPROTECTOR=y, guest kernel need random u64 and

require them from host kvm using hvc.

If FEAT_RNG is supported and EL3 firmware not support smccc trng, host

kvm finally return random u64 using RNDRRS to guest.

Shall we firstly let guest get random u64 from RNDRRS to avoid hvc trap?

For example, if host find smccc trng not available, then tell guest smccc

trng not available when guest check trng version.


Thanks for your help.

Nianyao