linux-kernel - Re: [PATCH v2 6/7] xen: allow mapping ACPI data using a different physical address

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Message-ID: <b6bb45ab-23bb-458d-a8db-9619f594e8c7@suse.com>
Date: Tue, 10 Sep 2024 10:15:34 +0200
From: Juergen Gross <jgross@...e.com>
To: Jan Beulich <jbeulich@...e.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "H. Peter Anvin" <hpa@...or.com>, "Rafael J. Wysocki" <rafael@...nel.org>,
 Len Brown <lenb@...nel.org>, Boris Ostrovsky <boris.ostrovsky@...cle.com>,
 xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
 x86@...nel.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v2 6/7] xen: allow mapping ACPI data using a different
 physical address

On 20.08.24 11:56, Jan Beulich wrote:
> On 20.08.2024 10:20, Juergen Gross wrote:
>> @@ -838,6 +839,31 @@ void __init xen_do_remap_nonram(void)
>>   	pr_info("Remapped %u non-RAM page(s)\n", remapped);
>>   }
>>   
>> +/*
>> + * Xen variant of acpi_os_ioremap() taking potentially remapped non-RAM
>> + * regions into acount.
>> + * Any attempt to map an area crossing a remap boundary will produce a
>> + * WARN() splat.
>> + */
>> +static void __iomem *xen_acpi_os_ioremap(acpi_physical_address phys,
>> +					 acpi_size size)
>> +{
>> +	unsigned int i;
>> +	struct nonram_remap *remap = xen_nonram_remap;
> 
> const (also in one of the functions in patch 5)?

Yes.

> 
>> +	for (i = 0; i < nr_nonram_remap; i++) {
>> +		if (phys + size > remap->maddr &&
>> +		    phys < remap->maddr + remap->size) {
>> +			WARN_ON(phys < remap->maddr ||
>> +				phys + size > remap->maddr + remap->size);
>> +			phys = remap->paddr + phys - remap->maddr;
>> +			break;
>> +		}
>> +	}
>> +
>> +	return x86_acpi_os_ioremap(phys, size);
>> +}
> 
> At least this, perhaps also what patch 5 adds, likely wants to be limited
> to the XEN_DOM0 case? Or else I wonder whether ...
> 
>> @@ -850,6 +876,10 @@ void __init xen_add_remap_nonram(phys_addr_t maddr, phys_addr_t paddr,
>>   		BUG();
>>   	}
>>   
>> +	/* Switch to the Xen acpi_os_ioremap() variant. */
>> +	if (nr_nonram_remap == 0)
>> +		acpi_os_ioremap = xen_acpi_os_ioremap;
> 
> ... this would actually build when XEN_DOM0=n.
> 
> I'm actually surprised there's no Dom0-only code section in this file,
> where the new code could then simply be inserted.

I'd rather make this conditional on CONFIG_ACPI.

Depending on how Xen tools will handle a PV-domain with "e820_host=1" this
code might be important for domUs, too.

Juergen

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