linux-kernel - Re: [Xen-devel] [RFC PATCH v4 1/7] xen/pvh: Split CONFIG_XEN_PVH into CONFIG_PVH and CONFIG_XEN

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Date:   Thu, 1 Mar 2018 06:43:10 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Maran Wilson <maran.wilson@...cle.com>
Cc:     pbonzini@...hat.com, boris.ostrovsky@...cle.com,
        roger.pau@...rix.com, andrew.cooper3@...rix.com, hch@...radead.org,
        JBeulich@...e.com, x86@...nel.org, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        thomas.lendacky@....com, dave.hansen@...ux.intel.com,
        rkrcmar@...hat.com, gregkh@...uxfoundation.org, mchehab@...nel.org,
        hpa@...or.com, linus.walleij@...aro.org, mingo@...hat.com,
        rdunlap@...radead.org, luto@...nel.org, jpoimboe@...hat.com,
        tglx@...utronix.de, bp@...e.de, davem@...emloft.net,
        kirill.shutemov@...ux.intel.com
Subject: Re: [Xen-devel] [RFC PATCH v4 1/7] xen/pvh: Split CONFIG_XEN_PVH into
 CONFIG_PVH and CONFIG_XEN_PVH

On 28/02/18 22:07, Konrad Rzeszutek Wilk wrote:
> On Wed, Feb 28, 2018 at 10:27:57AM -0800, Maran Wilson wrote:
>> In order to pave the way for hypervisors other then Xen to use the PVH
>> entry point for VMs, we need to factor the PVH entry code into Xen specific
>> and hypervisor agnostic components. The first step in doing that, is to
>> create a new config option for PVH entry that can be enabled
>> independently from CONFIG_XEN.
>>
>> Signed-off-by: Maran Wilson <maran.wilson@...cle.com>
>> ---
>>  arch/x86/Kconfig          | 8 ++++++++
>>  arch/x86/kernel/head_64.S | 4 ++--
>>  arch/x86/xen/Kconfig      | 3 ++-
>>  3 files changed, 12 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index eb7f43f23521..fa7cd0305125 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -791,6 +791,14 @@ config KVM_GUEST
>>  	  underlying device model, the host provides the guest with
>>  	  timing infrastructure such as time of day, and system time
>>  
>> +config PVH
>> +	bool "Support for running PVH guests"
>> +	depends on KVM_GUEST || XEN
>> +	def_bool n
>> +	---help---
>> +	  This option enables the PVH entry point for guest virtual machines
>> +	  as specified in the x86/HVM direct boot ABI.
>> +
>>  config KVM_DEBUG_FS
>>  	bool "Enable debug information for KVM Guests in debugfs"
>>  	depends on KVM_GUEST && DEBUG_FS
>> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
>> index 0f545b3cf926..fc9f678c6413 100644
>> --- a/arch/x86/kernel/head_64.S
>> +++ b/arch/x86/kernel/head_64.S
>> @@ -41,7 +41,7 @@
>>  
>>  #define pud_index(x)	(((x) >> PUD_SHIFT) & (PTRS_PER_PUD-1))
>>  
>> -#if defined(CONFIG_XEN_PV) || defined(CONFIG_XEN_PVH)
>> +#if defined(CONFIG_XEN_PV) || defined(CONFIG_PVH)
>>  PGD_PAGE_OFFSET = pgd_index(__PAGE_OFFSET_BASE)
>>  PGD_START_KERNEL = pgd_index(__START_KERNEL_map)
>>  #endif
>> @@ -387,7 +387,7 @@ NEXT_PAGE(early_dynamic_pgts)
>>  
>>  	.data
>>  
>> -#if defined(CONFIG_XEN_PV) || defined(CONFIG_XEN_PVH)
>> +#if defined(CONFIG_XEN_PV) || defined(CONFIG_PVH)
>>  NEXT_PGD_PAGE(init_top_pgt)
>>  	.quad   level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE_NOENC
>>  	.org    init_top_pgt + PGD_PAGE_OFFSET*8, 0
>> diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
>> index f605825a04ab..021c8591c3c0 100644
>> --- a/arch/x86/xen/Kconfig
>> +++ b/arch/x86/xen/Kconfig
>> @@ -77,8 +77,9 @@ config XEN_DEBUG_FS
>>  	  Enabling this option may incur a significant performance overhead.
>>  
>>  config XEN_PVH
>> -	bool "Support for running as a PVH guest"
>> +	bool "Support for running as a Xen PVH guest"
>>  	depends on XEN && XEN_PVHVM && ACPI
>>  	# Pre-built page tables are not ready to handle 5-level paging.
>>  	depends on !X86_5LEVEL
> 
> Not specific to this patch, but why is this there? PVH is not using PV so
> there should be no problems with 5 level paging.
> 
> Juergen, thoughts?

This dependency will be removed with Kyrill's series enabling to boot
the same kernel with either 5- or 4-level paging.

Adding 5-level paging support to the PVH boot path could be done later.
OTOH the same could be achieved by using grub2 to boot in PVH mode (with
my grub2 PVH series) as this variant is using the common Linux boot
entry, not the PVH specific one.


Juergen