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

[Zhenzhong Duan]

On 2019/6/25 20:31, Juergen Gross wrote:
> 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@xxxxxxxxxx>
> > Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> > Cc: Juergen Gross <jgross@xxxxxxxx>
> > Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Borislav Petkov <bp@xxxxxxxxx>
> > Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
> > ---
> > Â arch/x86/xen/enlighten_hvm.c | 18 ++++++++++++------
> > Â 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 @@
> > Â #include "mmu.h"
> > Â #include "smp.h"
> > Â +extern bool nopv;
> > Â static unsigned long shared_info_pfn;
> > Â Â void xen_hvm_init_shared_info(void)
> > @@ -226,20 +227,24 @@ static uint32_t __init xen_platform_hvm(void)
> > ÂÂÂÂÂ if (xen_pv_domain())
> > ÂÂÂÂÂÂÂÂÂ return 0;
> > Â +#ifdef CONFIG_XEN_PVH
> > +ÂÂÂ /* Test for PVH domain (PVH boot path taken overrides ACPI 
> > flags). */
> > +ÂÂÂ if (!x86_platform.legacy.rtc && x86_platform.legacy.no_vga)
> > +ÂÂÂÂÂÂÂ xen_pvh = true;
>
> Sorry, this won't work, as ACPI tables are scanned only some time later.
Hmm, right. Thanks for point out.
> 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.

After that warning, I guess PVH will run into hang finally? If it's 
true, BUG() is better?

Adding another hypervisor_x86 is a bit redundant, I think of below change.

I'll test it tomorrow. But appreciate your suggestion whether it's 
feasible. Thanks

--- a/arch/x86/xen/enlighten_hvm.c
+++ b/arch/x86/xen/enlighten_hvm.c
@@ -25,6 +25,7 @@
Â#include "mmu.h"
Â#include "smp.h"

+extern bool nopv;
Âstatic unsigned long shared_info_pfn;

Âvoid xen_hvm_init_shared_info(void)
@@ -221,11 +222,37 @@ bool __init xen_hvm_need_lapic(void)
ÂÂÂÂÂÂÂ return true;
Â}

+static __init void xen_hvm_nopv_guest_late_init(void)
+{
+#ifdef CONFIG_XEN_PVH
+ÂÂÂÂÂÂ if (x86_platform.legacy.rtc || !x86_platform.legacy.no_vga)
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ return;
+
+ÂÂÂÂÂÂ /* PVH detected. */
+ÂÂÂÂÂÂ xen_pvh = true;
+
+ÂÂÂÂÂÂ printk(KERN_CRIT "nopv parameter isn't supported in PVH guest\n");
+ÂÂÂÂÂÂ BUG();
+#endif
+}
+
+
Âstatic uint32_t __init xen_platform_hvm(void)
Â{
ÂÂÂÂÂÂÂ if (xen_pv_domain())
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ return 0;

+ÂÂÂÂÂÂ if (xen_pvh_domain() && nopv)
+ÂÂÂÂÂÂ {
+ÂÂÂÂÂÂ /* guest booting via the Xen-PVH boot entry goes here */
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ printk(KERN_INFO "nopv parameter is ignored in PVH 
guest\n");
+ÂÂÂÂÂÂ }
+ÂÂÂÂÂÂ else if (nopv)
+ÂÂÂÂÂÂ {
+ÂÂÂÂÂÂ /* guest booting via normal boot entry (like via grub2) goes here */
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ x86_init.hyper.guest_late_init = 
xen_hvm_nopv_guest_late_init;
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ return 0;
+ÂÂÂÂÂÂ }
ÂÂÂÂÂÂÂ return xen_cpuid_base();
Â}

@@ -258,4 +285,5 @@ static __init void xen_hvm_guest_late_init(void)
 .init.init_mem_mapping = xen_hvm_init_mem_mapping,
ÂÂÂÂÂÂÂ .init.guest_late_initÂÂ = xen_hvm_guest_late_init,
ÂÂÂÂÂÂÂ .runtime.pin_vcpuÂÂÂÂÂÂ = xen_pin_vcpu,
+ÂÂÂÂÂÂ .ignore_nopvÂÂÂÂÂÂÂÂÂÂÂ = true,
Â};