[RFC PATCH v1] powerpc/XIVE: SVM: share the event-queue page with the Hypervisor.

[Cédric Le Goater]

( Please use clg at kaod.org. I hardly use clg at fr.ibm.com.)

On 3/15/20 11:37 PM, Ram Pai wrote:
> XIVE interrupt controller maintains a Event-Queue(EQ) page. This page is
> used to communicate events with the Hypervisor/Qemu.

Here is an alternative for the above :

    XIVE interrupt controller use an Event Queue (EQ) to enqueue event 
    notifications when an exception occurs. The EQ is a single memory page 
    provided by the O/S defining a circular buffer, one per server and 
    priority couple.

    On baremetal, the EQ page is configured with an OPAL call. On pseries,
    an extra hop is necessary and the guest OS uses the hcall 
    H_INT_SET_QUEUE_CONFIG to configure the XIVE interrupt controller. 

> In Secure-VM, unless a page is shared with the Hypervisor, 
> the Hypervisor will not be able to read/write to that page.

This is a bit confusing to me as no software is involved when delivering 
the interrupt to the guest. When you are referring to the "Hypervisor", 
is it software and hardware ?  

If so, I would say:

    The XIVE controller being Hypervisor privileged, it will not be 
    allowed to enqueue event notifications for a Secure VM unless  
    the EQ pages are in the shared page pool.

> Explicitly share the EQ page with the Hypervisor, and unshare it
> during cleanup.  This enables SVM to use XIVE.

yes but KVM also needs support for the TIMA and ESB page fault handlers. 

> (NOTE: If the Hypervisor/Ultravisor is unable to target interrupts
>  directly to Secure VM, use "kernel_irqchip=off" on the qemu command
>  line).

So, I would say here :

   Hypervisor/Ultravisor still requires support for the TIMA and ESB page 
   fault handlers. Until this is complete, QEMU can use the emulated XIVE
   device for Secure VMs, option "kernel_irqchip=off" on the QEMU pseries 
   machine.

The rest looks good to me.

Thanks,

C. 

 
> Cc: kvm-ppc at vger.kernel.org
> Cc: linuxppc-dev at lists.ozlabs.org
> Cc: Michael Ellerman <mpe at ellerman.id.au>
> Cc: Thiago Jung Bauermann <bauerman at linux.ibm.com>
> Cc: Michael Anderson <andmike at linux.ibm.com>
> Cc: Sukadev Bhattiprolu <sukadev at linux.vnet.ibm.com>
> Cc: Alexey Kardashevskiy <aik at ozlabs.ru>
> Cc: Paul Mackerras <paulus at ozlabs.org>
> Cc: Greg Kurz <groug at kaod.org>
> Cc: Cedric Le Goater <clg at fr.ibm.com>
> Cc: David Gibson <david at gibson.dropbear.id.au>
> Signed-off-by: Ram Pai <linuxram at us.ibm.com>
> ---
>  arch/powerpc/sysdev/xive/spapr.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/powerpc/sysdev/xive/spapr.c b/arch/powerpc/sysdev/xive/spapr.c
> index 55dc61c..608b52f 100644
> --- a/arch/powerpc/sysdev/xive/spapr.c
> +++ b/arch/powerpc/sysdev/xive/spapr.c
> @@ -26,6 +26,8 @@
>  #include <asm/xive.h>
>  #include <asm/xive-regs.h>
>  #include <asm/hvcall.h>
> +#include <asm/svm.h>
> +#include <asm/ultravisor.h>
> 
>  #include "xive-internal.h"
> 
> @@ -501,6 +503,9 @@ static int xive_spapr_configure_queue(u32 target, struct xive_q *q, u8 prio,
>  		rc = -EIO;
>  	} else {
>  		q->qpage = qpage;
> +		if (is_secure_guest())
> +			uv_share_page(PHYS_PFN(qpage_phys),
> +					1 << xive_alloc_order(order));
>  	}
>  fail:
>  	return rc;
> @@ -534,6 +539,8 @@ static void xive_spapr_cleanup_queue(unsigned int cpu, struct xive_cpu *xc,
>  		       hw_cpu, prio);
> 
>  	alloc_order = xive_alloc_order(xive_queue_shift);
> +	if (is_secure_guest())
> +		uv_unshare_page(PHYS_PFN(__pa(q->qpage)), 1 << alloc_order);
>  	free_pages((unsigned long)q->qpage, alloc_order);
>  	q->qpage = NULL;
>  }
>