linux-kernel - Re: [RFC PATCH v3 2/2] KVM: x86: Allow Qemu/KVM to use PVH entry point

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Date:   Fri, 15 Dec 2017 16:55:46 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Maran Wilson <maran.wilson@...cle.com>, 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
Cc:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        rkrcmar@...hat.com
Subject: Re: [RFC PATCH v3 2/2] KVM: x86: Allow Qemu/KVM to use PVH entry
 point

On 13/12/17 00:42, Maran Wilson wrote:
> For certain applications it is desirable to rapidly boot a KVM virtual
> machine. In cases where legacy hardware and software support within the
> guest is not needed, Qemu should be able to boot directly into the
> uncompressed Linux kernel binary without the need to run firmware.
> 
> There already exists an ABI to allow this for Xen PVH guests and the ABI
> is supported by Linux and FreeBSD:
> 
>    https://xenbits.xen.org/docs/unstable/misc/pvh.html
> 
> This patch enables Qemu to use that same entry point for booting KVM
> guests.

I'm fine with the general idea.

I'm wondering whether you really want to require CONFIG_XEN for the
KVM case, though.

Wouldn't it be better to rename arch/x86/xen/enlighten_pvh.c to
arch/x86/pvh.c and arch/x86/xen/xen-pvh.S to arch/x86/pvh-head.S,
put both under CONFIG_PVH umbrella and select this from CONFIG_XEN_PVH
and KVM_PVH (or what you like to call it)?

In the two moved source files you can make Xen/KVM-specific parts
optional via their CONFIG_ options.

And you might want to add an own ELF note for the KVM case?

> ---
>  arch/x86/xen/enlighten_pvh.c | 51 +++++++++++++++++++++++++++++++-------------
>  1 file changed, 36 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/x86/xen/enlighten_pvh.c b/arch/x86/xen/enlighten_pvh.c
> index 98ab176..12f3716 100644
> --- a/arch/x86/xen/enlighten_pvh.c
> +++ b/arch/x86/xen/enlighten_pvh.c
> @@ -31,21 +31,38 @@ static void xen_pvh_arch_setup(void)
>  		acpi_irq_model = ACPI_IRQ_MODEL_PLATFORM;
>  }
>  
> -static void __init init_pvh_bootparams(void)
> +static void __init init_pvh_bootparams(bool xen_guest)
>  {
>  	struct xen_memory_map memmap;
>  	int rc;
>  
>  	memset(&pvh_bootparams, 0, sizeof(pvh_bootparams));
>  
> -	memmap.nr_entries = ARRAY_SIZE(pvh_bootparams.e820_table);
> -	set_xen_guest_handle(memmap.buffer, pvh_bootparams.e820_table);
> -	rc = HYPERVISOR_memory_op(XENMEM_memory_map, &memmap);
> -	if (rc) {
> -		xen_raw_printk("XENMEM_memory_map failed (%d)\n", rc);
> +	if ((pvh_start_info.version > 0) && (pvh_start_info.memmap_entries)) {
> +		struct hvm_memmap_table_entry *ep;
> +		int i;
> +
> +		ep = __va(pvh_start_info.memmap_paddr);
> +		pvh_bootparams.e820_entries = pvh_start_info.memmap_entries;
> +
> +		for (i = 0; i < pvh_bootparams.e820_entries ; i++, ep++) {
> +			pvh_bootparams.e820_table[i].addr = ep->addr;
> +			pvh_bootparams.e820_table[i].size = ep->size;
> +			pvh_bootparams.e820_table[i].type = ep->type;
> +		}
> +	} else if (xen_guest) {
> +		memmap.nr_entries = ARRAY_SIZE(pvh_bootparams.e820_table);
> +		set_xen_guest_handle(memmap.buffer, pvh_bootparams.e820_table);
> +		rc = HYPERVISOR_memory_op(XENMEM_memory_map, &memmap);
> +		if (rc) {
> +			xen_raw_printk("XENMEM_memory_map failed (%d)\n", rc);
> +			BUG();
> +		}
> +		pvh_bootparams.e820_entries = memmap.nr_entries;
> +	} else {
> +		xen_raw_printk("Error: Could not find memory map\n");

xen_raw_printk() without being a Xen guest?


Juergen