Re: [PATCH v2 5/7] x86/xen: nopv parameter support for HVM guest

From: Juergen Gross <jgross@suse.com>
To: Zhenzhong Duan <zhenzhong.duan@oracle.com>, linux-kernel@vger.kernel.org
Cc: tglx@linutronix.de, mingo@kernel.org, bp@alien8.de,
	hpa@zytor.com, boris.ostrovsky@oracle.com,
	sstabellini@kernel.org, peterz@infradead.org,
	srinivas.eeda@oracle.com, Ingo Molnar <mingo@redhat.com>,
	xen-devel@lists.xenproject.org
Subject: Re: [PATCH v2 5/7] x86/xen: nopv parameter support for HVM guest
Date: Tue, 25 Jun 2019 14:31:05 +0200	[thread overview]
Message-ID: <99a28880-c2bf-e328-ee52-afc782af3b74@suse.com> (raw)
In-Reply-To: <1561377779-28036-6-git-send-email-zhenzhong.duan@oracle.com>

On 24.06.19 14:02, Zhenzhong Duan wrote:
> PVH guest needs PV extentions to work, so nopv parameter is ignored
> for PVH but not for HVM guest.
> 
> In order for nopv parameter to take effect for HVM guest, we need to
> distinguish between PVH and HVM guest early in hypervisor detection
> code. By moving the detection of PVH in xen_platform_hvm(),
> xen_pvh_domain() could be used for that purpose.
> 
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: Juergen Gross <jgross@suse.com>
> Cc: Stefano Stabellini <sstabellini@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: xen-devel@lists.xenproject.org
> ---
>   arch/x86/xen/enlighten_hvm.c | 18 ++++++++++++------
>   1 file changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
> index 7fcb4ea..26939e7 100644
> --- a/arch/x86/xen/enlighten_hvm.c
> +++ b/arch/x86/xen/enlighten_hvm.c
> @@ -25,6 +25,7 @@
>   #include "mmu.h"
>   #include "smp.h"
>   
> +extern bool nopv;
>   static unsigned long shared_info_pfn;
>   
>   void xen_hvm_init_shared_info(void)
> @@ -226,20 +227,24 @@ static uint32_t __init xen_platform_hvm(void)
>   	if (xen_pv_domain())
>   		return 0;
>   
> +#ifdef CONFIG_XEN_PVH
> +	/* Test for PVH domain (PVH boot path taken overrides ACPI flags). */
> +	if (!x86_platform.legacy.rtc && x86_platform.legacy.no_vga)
> +		xen_pvh = true;

Sorry, this won't work, as ACPI tables are scanned only some time later.

You can test for xen_pvh being true here (for the case where the guest
has been booted via the Xen-PVH boot entry) and handle that case, but
the case of a PVH guest started via the normal boot entry (like via
grub2) and nopv specified is difficult. The only idea I have right now
would be to use another struct hypervisor_x86 for that case which will
only be used for Xen HVM/PVH _and_ nopv specified. It should be a copy
of the bare metal variant, but a special guest_late_init member issuing
a big fat warning in case PVH is being detected.

Juergen