Re: [PATCH V2 4/4] arm/xen: Read extended regions from DT and init Xen resource
From: Stefano Stabellini <sstabellini@kernel.org>
Date: 2021-10-28 01:40:12
Also in:
lkml, xen-devel
On Tue, 26 Oct 2021, Oleksandr Tyshchenko wrote:
quoted hunk ↗ jump to hunk
From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com> This patch implements arch_xen_unpopulated_init() on Arm where the extended regions (if any) are gathered from DT and inserted into passed 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@epam.com> --- Changes RFC -> V2: - new patch, instead of "[RFC PATCH 2/2] xen/unpopulated-alloc: Query hypervisor to provide unallocated space" --- arch/arm/xen/enlighten.c | 112 +++++++++++++++++++++++++++++++++++++++++++++++ drivers/xen/Kconfig | 2 +- 2 files changed, 113 insertions(+), 1 deletion(-)diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c index dea46ec..1a1e0d3 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 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 +304,117 @@ static void __init xen_acpi_guest_init(void) #endif } +#ifdef CONFIG_XEN_UNPOPULATED_ALLOC +int 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; + struct range mhp_range; + int rc; + + if (!xen_domain()) + 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; + } + + /* Check whether the resource range is within the hotpluggable range */ + mhp_range = mhp_get_pluggable_range(true); + if (min_gpaddr < mhp_range.start) + min_gpaddr = mhp_range.start; + if (max_gpaddr > mhp_range.end) + max_gpaddr = mhp_range.end; + + res->start = min_gpaddr; + res->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; + + start = regs[i - 1].end + 1; + end = regs[i].start - 1; + + if (start > (end + 1)) {
Should this be: if (start >= end) ?
+ rc = -EINVAL; + goto err; + } + + /* There is no hole between regions */ + if (start == (end + 1))
Also here, shouldn't it be: if (start == end) ? I think I am missing again something in termination accounting :-)
+ continue;
+
+ /* Check whether the hole range is within the resource range */
+ if (start < res->start || end > res->end) {By definition I don't think this check is necessary as either condition is impossible?
+ if (start < res->start)
+ start = res->start;
+ if (end > res->end)
+ end = res->end;
+
+ if (start >= (end + 1))
+ continue;
+ }
+
+ 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;Do we need to set any flags so that the system can reuse the memory in the hole, e.g. IORESOURCE_MEM? Or is it not necessary?
+ rc = insert_resource(res, tmp_res);
+ if (rc) {
+ pr_err("Cannot insert resource [%llx - %llx] %d\n",
+ tmp_res->start, tmp_res->end, rc);
Although it is impossible to enable XEN_UNPOPULATED_ALLOC on arm32 due
to unmet dependencies, I would like to keep the implementation of
arch_xen_unpopulated_init 32bit clean.
I am getting build errors like (by forcing arch_xen_unpopulated_init to
compile on arm32):
./include/linux/kern_levels.h:5:18: warning: format ‘%llx’ expects argument of type ‘long long unsigned int’, but argument 3 has type ‘resource_size_t {aka unsigned int}’ [-Wformat=]
quoted hunk ↗ jump to hunk
+ kfree(tmp_res); + goto err; + } + } + +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 1b2c3ac..e6031fc 100644 --- a/drivers/xen/Kconfig +++ b/drivers/xen/Kconfig@@ -297,7 +297,7 @@ 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