From mboxrd@z Thu Jan 1 00:00:00 1970 From: marc.zyngier@arm.com (Marc Zyngier) Date: Fri, 26 Apr 2013 16:54:01 +0100 Subject: [PATCH 0/2] Early printk support for virtio console devices. In-Reply-To: <201304261703.17798.arnd@arndb.de> References: <1366974299-17877-1-git-send-email-pranavkumar@linaro.org> <1577576.O1Cm2pf5KD@wuerfel> <201304261703.17798.arnd@arndb.de> Message-ID: <517AA319.5070709@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 26/04/13 16:03, Arnd Bergmann wrote: > On Friday 26 April 2013, Anup Patel wrote: >> I am curious about how smh-based or hypercall-based early prints would >> be handled in following scenario: >> >> "A board is running KVM ARM enabled kernel and linux console on serial >> port. Now a user remotely connects to the board via telnet/ssh and >> launches a VM with smh-based or hypercall-based earlyprintk." >> >> In the above scenario, will smh-based or hypercall-based earlyprints >> appear to user on remote shell or not ? > > The implementation of the console device would still be done by KVM, > as for any other virtual device, so it shows up whereever kvm is > configured to output the console data. Actually, at least in the case of smh-based earlyprintk, the output only appears in the model console, and never reach the rest of the kernel. And any other non-MMIO approach (like a hypercall) will be very hard to feed back to the console, as KVM itself has no idea of what a "console" is. You'd need another side channel to userspace, hoping that it will be able to merge the multiple streams. M. -- Jazz is not dead. It just smells funny...