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Message-ID: <alpine.DEB.2.22.394.2111241551450.1412361@ubuntu-linux-20-04-desktop>
Date: Wed, 24 Nov 2021 17:07:09 -0800 (PST)
From: Stefano Stabellini <sstabellini@...nel.org>
To: Oleksandr Tyshchenko <olekstysh@...il.com>
cc: xen-devel@...ts.xenproject.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Juergen Gross <jgross@...e.com>,
Stefano Stabellini <sstabellini@...nel.org>,
Russell King <linux@...linux.org.uk>,
Julien Grall <julien@....org>
Subject: Re: [PATCH V3 5/6] arm/xen: Read extended regions from DT and init
Xen resource
On Wed, 24 Nov 2021, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
>
> This patch implements arch_xen_unpopulated_init() on Arm where
> the extended regions (if any) are gathered from DT and inserted
> into specific Xen resource to be used as unused address space
> for Xen scratch pages by unpopulated-alloc code.
>
> The extended region (safe range) is a region of guest physical
> address space which is unused and could be safely used to create
> grant/foreign mappings instead of wasting real RAM pages from
> the domain memory for establishing these mappings.
>
> The extended regions are chosen by the hypervisor at the domain
> creation time and advertised to it via "reg" property under
> hypervisor node in the guest device-tree. As region 0 is reserved
> for grant table space (always present), the indexes for extended
> regions are 1...N.
>
> If arch_xen_unpopulated_init() fails for some reason the default
> behaviour will be restored (allocate xenballooned pages).
>
> This patch also removes XEN_UNPOPULATED_ALLOC dependency on x86.
>
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
Reviewed-by: Stefano Stabellini <sstabellini@...nel.org>
> ---
> Changes RFC -> V2:
> - new patch, instead of
> "[RFC PATCH 2/2] xen/unpopulated-alloc: Query hypervisor to provide unallocated space"
>
> Changes V2 -> V3:
> - update comments in code
> - drop the checks that a region is within the hotpluggable range,
> now the common code takes care of
> - update arch_xen_unpopulated_init() according to interface change,
> move xen_resource here, etc
> - use %pR specifier in error message
> - bait out in arch_xen_unpopulated_init() if !acpi_disabled
> - update checks in second loop in arch_xen_unpopulated_init()
> for the sake of clarity
> ---
> arch/arm/xen/enlighten.c | 106 +++++++++++++++++++++++++++++++++++++++++++++++
> drivers/xen/Kconfig | 2 +-
> 2 files changed, 107 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> index 3fb3384..019caa6 100644
> --- a/arch/arm/xen/enlighten.c
> +++ b/arch/arm/xen/enlighten.c
> @@ -62,6 +62,7 @@ static __read_mostly unsigned int xen_events_irq;
> static __read_mostly phys_addr_t xen_grant_frames;
>
> #define GRANT_TABLE_INDEX 0
> +#define EXT_REGION_INDEX 1
>
> uint32_t xen_start_flags;
> EXPORT_SYMBOL(xen_start_flags);
> @@ -303,6 +304,111 @@ static void __init xen_acpi_guest_init(void)
> #endif
> }
>
> +#ifdef CONFIG_XEN_UNPOPULATED_ALLOC
> +/*
> + * A type-less specific Xen resource which contains extended regions
> + * (unused regions of guest physical address space provided by the hypervisor).
> + */
> +static struct resource xen_resource = {
> + .name = "Xen unused space",
> +};
> +
> +int __init arch_xen_unpopulated_init(struct resource **res)
> +{
> + struct device_node *np;
> + struct resource *regs, *tmp_res;
> + uint64_t min_gpaddr = -1, max_gpaddr = 0;
> + unsigned int i, nr_reg = 0;
> + int rc;
> +
> + if (!xen_domain())
> + return -ENODEV;
> +
> + if (!acpi_disabled)
> + return -ENODEV;
> +
> + np = of_find_compatible_node(NULL, NULL, "xen,xen");
> + if (WARN_ON(!np))
> + return -ENODEV;
> +
> + /* Skip region 0 which is reserved for grant table space */
> + while (of_get_address(np, nr_reg + EXT_REGION_INDEX, NULL, NULL))
> + nr_reg++;
> +
> + if (!nr_reg) {
> + pr_err("No extended regions are found\n");
> + return -EINVAL;
> + }
> +
> + regs = kcalloc(nr_reg, sizeof(*regs), GFP_KERNEL);
> + if (!regs)
> + return -ENOMEM;
> +
> + /*
> + * Create resource from extended regions provided by the hypervisor to be
> + * used as unused address space for Xen scratch pages.
> + */
> + for (i = 0; i < nr_reg; i++) {
> + rc = of_address_to_resource(np, i + EXT_REGION_INDEX, ®s[i]);
> + if (rc)
> + goto err;
> +
> + if (max_gpaddr < regs[i].end)
> + max_gpaddr = regs[i].end;
> + if (min_gpaddr > regs[i].start)
> + min_gpaddr = regs[i].start;
> + }
> +
> + xen_resource.start = min_gpaddr;
> + xen_resource.end = max_gpaddr;
> +
> + /*
> + * Mark holes between extended regions as unavailable. The rest of that
> + * address space will be available for the allocation.
> + */
> + for (i = 1; i < nr_reg; i++) {
> + resource_size_t start, end;
> +
> + /* There is an overlap between regions */
> + if (regs[i - 1].end + 1 > regs[i].start) {
> + rc = -EINVAL;
> + goto err;
> + }
> +
> + /* There is no hole between regions */
> + if (regs[i - 1].end + 1 == regs[i].start)
> + continue;
> +
> + start = regs[i - 1].end + 1;
> + end = regs[i].start - 1;
> +
> + tmp_res = kzalloc(sizeof(*tmp_res), GFP_KERNEL);
> + if (!tmp_res) {
> + rc = -ENOMEM;
> + goto err;
> + }
> +
> + tmp_res->name = "Unavailable space";
> + tmp_res->start = start;
> + tmp_res->end = end;
> +
> + rc = insert_resource(&xen_resource, tmp_res);
> + if (rc) {
> + pr_err("Cannot insert resource %pR (%d)\n", tmp_res, rc);
> + kfree(tmp_res);
> + goto err;
> + }
> + }
> +
> + *res = &xen_resource;
> +
> +err:
> + kfree(regs);
> +
> + return rc;
> +}
> +#endif
> +
> static void __init xen_dt_guest_init(void)
> {
> struct device_node *xen_node;
> diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
> index a1b11c62..553b614 100644
> --- a/drivers/xen/Kconfig
> +++ b/drivers/xen/Kconfig
> @@ -321,7 +321,7 @@ config XEN_FRONT_PGDIR_SHBUF
>
> config XEN_UNPOPULATED_ALLOC
> bool "Use unpopulated memory ranges for guest mappings"
> - depends on X86 && ZONE_DEVICE
> + depends on ZONE_DEVICE
> default XEN_BACKEND || XEN_GNTDEV || XEN_DOM0
> help
> Use unpopulated memory ranges in order to create mappings for guest
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