KVM Archive on lore.kernel.org
 help / color / Atom feed
From: Mark Rutland <mark.rutland@arm.com>
To: Andrew Jones <drjones@redhat.com>
Cc: kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, maz@kernel.org
Subject: Re: [PATCH v2] arm64: KVM: Only skip MMIO insn once
Date: Thu, 22 Aug 2019 12:59:23 +0100
Message-ID: <20190822115923.GA33080@lakrids.cambridge.arm.com> (raw)
In-Reply-To: <20190822110305.18035-1-drjones@redhat.com>

On Thu, Aug 22, 2019 at 01:03:05PM +0200, Andrew Jones wrote:
> If after an MMIO exit to userspace a VCPU is immediately run with an
> immediate_exit request, such as when a signal is delivered or an MMIO
> emulation completion is needed, then the VCPU completes the MMIO
> emulation and immediately returns to userspace. As the exit_reason
> does not get changed from KVM_EXIT_MMIO in these cases we have to
> be careful not to complete the MMIO emulation again, when the VCPU is
> eventually run again, because the emulation does an instruction skip
> (and doing too many skips would be a waste of guest code :-) We need
> to use additional VCPU state to track if the emulation is complete.
> As luck would have it, we already have 'mmio_needed', which even
> appears to be used in this way by other architectures already.
> 
> Fixes: 0d640732dbeb ("arm64: KVM: Skip MMIO insn after emulation")
> Signed-off-by: Andrew Jones <drjones@redhat.com>

Ouch; sorry about this!

I haven't dug too deeply, but from the commit message, the below makes
sense to me. FWIW:

Acked-by: Mark Rutland <mark.rutland@arm.com>

Mark.

> ---
> v2: move mmio_needed use closer to other mmio state use [maz]
> 
>  virt/kvm/arm/mmio.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/virt/kvm/arm/mmio.c b/virt/kvm/arm/mmio.c
> index a8a6a0c883f1..6af5c91337f2 100644
> --- a/virt/kvm/arm/mmio.c
> +++ b/virt/kvm/arm/mmio.c
> @@ -86,6 +86,12 @@ int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  	unsigned int len;
>  	int mask;
>  
> +	/* Detect an already handled MMIO return */
> +	if (unlikely(!vcpu->mmio_needed))
> +		return 0;
> +
> +	vcpu->mmio_needed = 0;
> +
>  	if (!run->mmio.is_write) {
>  		len = run->mmio.len;
>  		if (len > sizeof(unsigned long))
> @@ -188,6 +194,7 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
>  	run->mmio.is_write	= is_write;
>  	run->mmio.phys_addr	= fault_ipa;
>  	run->mmio.len		= len;
> +	vcpu->mmio_needed	= 1;
>  
>  	if (!ret) {
>  		/* We handled the access successfully in the kernel. */
> -- 
> 2.18.1
> 

  reply index

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-22 11:03 Andrew Jones
2019-08-22 11:59 ` Mark Rutland [this message]
2019-08-22 12:21 ` Marc Zyngier

Reply instructions:

You may reply publically 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=20190822115923.GA33080@lakrids.cambridge.arm.com \
    --to=mark.rutland@arm.com \
    --cc=drjones@redhat.com \
    --cc=kvm@vger.kernel.org \
    --cc=kvmarm@lists.cs.columbia.edu \
    --cc=maz@kernel.org \
    /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

KVM Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/kvm/0 kvm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 kvm kvm/ https://lore.kernel.org/kvm \
		kvm@vger.kernel.org kvm@archiver.kernel.org
	public-inbox-index kvm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.kvm


AGPL code for this site: git clone https://public-inbox.org/ public-inbox