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

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Date:   Wed, 26 Jun 2019 16:56:46 +0800
From:   Zhenzhong Duan <zhenzhong.duan@...cle.com>
To:     Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org
Cc:     tglx@...utronix.de, mingo@...nel.org, bp@...en8.de, hpa@...or.com,
        boris.ostrovsky@...cle.com, sstabellini@...nel.org,
        peterz@...radead.org, srinivas.eeda@...cle.com,
        Ingo Molnar <mingo@...hat.com>, xen-devel@...ts.xenproject.org
Subject: Re: [PATCH v2 5/7] x86/xen: nopv parameter support for HVM guest


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@...cle.com>
>> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
>> Cc: Juergen Gross <jgross@...e.com>
>> Cc: Stefano Stabellini <sstabellini@...nel.org>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: Ingo Molnar <mingo@...hat.com>
>> Cc: Borislav Petkov <bp@...en8.de>
>> Cc: xen-devel@...ts.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.
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 @@
  #include "mmu.h"
  #include "smp.h"

+extern bool nopv;
  static unsigned long shared_info_pfn;

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

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

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

@@ -258,4 +285,5 @@ static __init void xen_hvm_guest_late_init(void)
         .init.init_mem_mapping  = xen_hvm_init_mem_mapping,
         .init.guest_late_init   = xen_hvm_guest_late_init,
         .runtime.pin_vcpu       = xen_pin_vcpu,
+       .ignore_nopv            = true,
  };