From: Alexandru Elisei <alexandru.elisei@arm.com>
To: Marc Zyngier <maz@kernel.org>,
linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
kvmarm@lists.cs.columbia.edu
Cc: James Morse <james.morse@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
kernel-team@android.com, stable@vger.kernel.org
Subject: Re: [PATCH] KVM: arm64: Fully zero the vcpu state on reset
Date: Thu, 8 Apr 2021 16:36:40 +0100 [thread overview]
Message-ID: <c34842b2-215a-e9d0-7d9d-a8cd64ed1171@arm.com> (raw)
In-Reply-To: <20210407181308.2265808-1-maz@kernel.org>
Hi Marc,
On 4/7/21 7:13 PM, Marc Zyngier wrote:
> On vcpu reset, we expect all the registers to be brought back
> to their initial state, which happens to be a bunch of zeroes.
>
> However, some recent commit broke this, and is now leaving a bunch
> of registers (such as a FP state) with whatever was left by the
> guest. My bad.
>
> Just zero the whole vcpu context on reset. It is more than we
> strictly need, but at least we won't miss anything. This also
> zeroes the __hyp_running_vcpu pointer, which is always NULL
> for a vcpu anyway.
Had a look at struct kvm_cpu_context and indeed the only field which doesn't
represent a guest register is __hyp_running_vcpu. Did a grep for all the places
where __hyp_running_vcpu is used, and indeed the assumption is that for a guest
the pointer is NULL, as __sysreg_restore_el1_state() relies on it.
>
> Cc: stable@vger.kernel.org
> Fixes: e47c2055c68e ("KVM: arm64: Make struct kvm_regs userspace-only")
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
> arch/arm64/kvm/reset.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> index bd354cd45d28..ef1c49a1a3ad 100644
> --- a/arch/arm64/kvm/reset.c
> +++ b/arch/arm64/kvm/reset.c
> @@ -240,8 +240,8 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
> break;
> }
>
> - /* Reset core registers */
> - memset(vcpu_gp_regs(vcpu), 0, sizeof(*vcpu_gp_regs(vcpu)));
> + /* Zero all registers */
> + memset(&vcpu->arch.ctxt, 0, sizeof(vcpu->arch.ctxt));
Checked that code earlier in the function does not touch the guest registers from
vcpu->arch.ctxt, to make sure we're not overwriting other reset values by mistake.
Looks good to me:
Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>
Thanks,
Alex
> vcpu_gp_regs(vcpu)->pstate = pstate;
>
> /* Reset system registers */
next prev parent reply other threads:[~2021-04-08 15:36 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-07 18:13 [PATCH] KVM: arm64: Fully zero the vcpu state on reset Marc Zyngier
2021-04-08 15:36 ` Alexandru Elisei [this message]
2021-04-09 17:18 ` Marc Zyngier
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=c34842b2-215a-e9d0-7d9d-a8cd64ed1171@arm.com \
--to=alexandru.elisei@arm.com \
--cc=james.morse@arm.com \
--cc=kernel-team@android.com \
--cc=kvm@vger.kernel.org \
--cc=kvmarm@lists.cs.columbia.edu \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=maz@kernel.org \
--cc=stable@vger.kernel.org \
--cc=suzuki.poulose@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).