Re: [PATCH 1/3 V4] kvm tools: Add memory gap for larger RAM sizes

[Asias He <asias.hejun@gmail.com>]

On 05/11/2011 11:17 PM, levinsasha928@gmail.com wrote:
> From: Sasha Levin <levinsasha928@gmail.com>
> 
> e820 is expected to leave a memory gap within the low 32
> bits of RAM space. From the documentation of e820_setup_gap():
> /*
>  * Search for the biggest gap in the low 32 bits of the e820
>  * memory space.  We pass this space to PCI to assign MMIO resources
>  * for hotplug or unconfigured devices in.
>  * Hopefully the BIOS let enough space left.
>  */
> 
> Not leaving such gap causes errors and hangs during the boot
> process.
> 
> This patch adds a memory gap between 0xe0000000 and 0x100000000
> when using more than 0xe0000000 bytes for guest RAM.
> 
> This patch updates the e820 table, slot allocations
> used for KVM_SET_USER_MEMORY_REGION.
> 
> Changes in V2:
>  - Allocate RAM with the gap to avoid altering the translation code.
>  - New patch description.
> 
> Changes in V3:
>  - Remove unnecessary casts.
> 
> Changes in V4:
>  - Rewrite kvm__init_ram().
>  - Document the 64bit gap within the code.
> 
> Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
> ---
>  tools/kvm/bios.c             |   27 ++++++++++++----
>  tools/kvm/include/kvm/e820.h |    2 +-
>  tools/kvm/include/kvm/kvm.h  |    2 +
>  tools/kvm/kvm.c              |   66 +++++++++++++++++++++++++++++++++++++----
>  4 files changed, 82 insertions(+), 15 deletions(-)
> 
> diff --git a/tools/kvm/bios.c b/tools/kvm/bios.c
> index 2199c0c..3cd9b24 100644
> --- a/tools/kvm/bios.c
> +++ b/tools/kvm/bios.c
> @@ -61,8 +61,6 @@ static void e820_setup(struct kvm *kvm)
>  	size		= guest_flat_to_host(kvm, E820_MAP_SIZE);
>  	mem_map		= guest_flat_to_host(kvm, E820_MAP_START);
>  
> -	*size		= E820_MEM_AREAS;
> -
>  	mem_map[i++]	= (struct e820_entry) {
>  		.addr		= REAL_MODE_IVT_BEGIN,
>  		.size		= EBDA_START - REAL_MODE_IVT_BEGIN,
> @@ -78,13 +76,28 @@ static void e820_setup(struct kvm *kvm)
>  		.size		= MB_BIOS_END - MB_BIOS_BEGIN,
>  		.type		= E820_MEM_RESERVED,
>  	};
> -	mem_map[i++]	= (struct e820_entry) {
> -		.addr		= BZ_KERNEL_START,
> -		.size		= kvm->ram_size - BZ_KERNEL_START,
> -		.type		= E820_MEM_USABLE,
> -	};
> +	if (kvm->ram_size < KVM_32BIT_GAP_START) {
> +		mem_map[i++]	= (struct e820_entry) {
> +			.addr		= BZ_KERNEL_START,
> +			.size		= kvm->ram_size - BZ_KERNEL_START,
> +			.type		= E820_MEM_USABLE,
> +		};
> +	} else {
> +		mem_map[i++]	= (struct e820_entry) {
> +			.addr		= BZ_KERNEL_START,
> +			.size		= KVM_32BIT_GAP_START - BZ_KERNEL_START,
> +			.type		= E820_MEM_USABLE,
> +		};
> +		mem_map[i++]	= (struct e820_entry) {
> +			.addr		= 0x100000000ULL,
> +			.size		= kvm->ram_size - KVM_32BIT_GAP_START,
> +			.type		= E820_MEM_USABLE,
> +		};
> +	}
>  
>  	BUILD_BUG_ON(i > E820_MEM_AREAS);
> +
> +	*size			= i;
>  }
>  
>  /**
> diff --git a/tools/kvm/include/kvm/e820.h b/tools/kvm/include/kvm/e820.h
> index 252ae1f..e0f5f2a 100644
> --- a/tools/kvm/include/kvm/e820.h
> +++ b/tools/kvm/include/kvm/e820.h
> @@ -8,7 +8,7 @@
>  #define E820_MEM_USABLE		1
>  #define E820_MEM_RESERVED	2
>  
> -#define E820_MEM_AREAS		4
> +#define E820_MEM_AREAS		5
>  
>  struct e820_entry {
>  	u64	addr;	/* start of memory segment */
> diff --git a/tools/kvm/include/kvm/kvm.h b/tools/kvm/include/kvm/kvm.h
> index 3dab78d..5e2e64c 100644
> --- a/tools/kvm/include/kvm/kvm.h
> +++ b/tools/kvm/include/kvm/kvm.h
> @@ -8,6 +8,8 @@
>  #include <time.h>
>  
>  #define KVM_NR_CPUS		(255)
> +#define KVM_32BIT_GAP_SIZE	(512 << 20)
> +#define KVM_32BIT_GAP_START	((1ULL << 32) - KVM_32BIT_GAP_SIZE)
>  
>  struct kvm {
>  	int			sys_fd;		/* For system ioctls(), i.e. /dev/kvm */
> diff --git a/tools/kvm/kvm.c b/tools/kvm/kvm.c
> index 65793f2..a3d3dd8 100644
> --- a/tools/kvm/kvm.c
> +++ b/tools/kvm/kvm.c
> @@ -153,23 +153,64 @@ static bool kvm__cpu_supports_vm(void)
>  	return regs.ecx & (1 << feature);
>  }
>  
> -void kvm__init_ram(struct kvm *self)
> +static void kvm_register_mem_slot(struct kvm *kvm, u32 slot, u64 guest_phys, u64 size, void *userspace_addr)
>  {
>  	struct kvm_userspace_memory_region mem;
>  	int ret;
>  
>  	mem = (struct kvm_userspace_memory_region) {
> -		.slot			= 0,
> -		.guest_phys_addr	= 0x0UL,
> -		.memory_size		= self->ram_size,
> -		.userspace_addr		= (unsigned long) self->ram_start,
> +		.slot			= slot,
> +		.guest_phys_addr	= guest_phys,
> +		.memory_size		= size,
> +		.userspace_addr		= (u64)userspace_addr,


I am seeing:

  CC       kvm.o
kvm.c: In function ‘kvm_register_mem_slot’:
kvm.c:165:22: error: cast from pointer to integer of different size
[-Werror=pointer-to-int-cast]
cc1: all warnings being treated as errors

make: *** [kvm.o] Error 1

with this patch on 32-bit box.


>  	};
>  
> -	ret = ioctl(self->vm_fd, KVM_SET_USER_MEMORY_REGION, &mem);
> +	ret = ioctl(kvm->vm_fd, KVM_SET_USER_MEMORY_REGION, &mem);
>  	if (ret < 0)
>  		die_perror("KVM_SET_USER_MEMORY_REGION ioctl");
>  }
>  
> +/*
> + * Allocating RAM size bigger than 4GB requires us to leave a gap
> + * in the RAM which is used for PCI MMIO, hotplug, and unconfigured
> + * devices (see documentation of e820_setup_gap() for details).
> + *
> + * If we're required to initialize RAM bigger than 4GB, we will create
> + * a gap between 0xe0000000 and 0x100000000 in the guest virtual mem space.
> + */
> +
> +void kvm__init_ram(struct kvm *self)
> +{
> +	u64	phys_start, phys_size;
> +	void	*host_mem;
> +
> +	if (self->ram_size < KVM_32BIT_GAP_START) {
> +		/* Use a single block of RAM for 32bit RAM */
> +
> +		phys_start = 0;
> +		phys_size  = self->ram_size;
> +		host_mem   = self->ram_start;
> +
> +		kvm_register_mem_slot(self, 0, 0, self->ram_size, self->ram_start);
> +	} else {
> +		/* First RAM range from zero to the PCI gap: */
> +
> +		phys_start = 0;
> +		phys_size  = KVM_32BIT_GAP_START;
> +		host_mem   = self->ram_start;
> +
> +		kvm_register_mem_slot(self, 0, phys_start, phys_size, host_mem);
> +
> +		/* Second RAM range from 4GB to the end of RAM: */
> +
> +		phys_start = 0x100000000ULL;
> +		phys_size  = self->ram_size - phys_size;
> +		host_mem   = self->ram_start + phys_start;
> +
> +		kvm_register_mem_slot(self, 1, phys_start, phys_size, host_mem);
> +	}
> +}
> +
>  int kvm__max_cpus(struct kvm *self)
>  {
>  	int ret;
> @@ -225,7 +266,18 @@ struct kvm *kvm__init(const char *kvm_dev, unsigned long ram_size)
>  
>  	self->ram_size		= ram_size;
>  
> -	self->ram_start = mmap(NULL, ram_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE, -1, 0);
> +	if (self->ram_size < KVM_32BIT_GAP_START) {
> +		self->ram_start = mmap(NULL, ram_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE, -1, 0);
> +	} else {
> +		self->ram_start = mmap(NULL, ram_size + KVM_32BIT_GAP_SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE, -1, 0);
> +		if (self->ram_start != MAP_FAILED) {
> +			/*
> +			 * We mprotect the gap (see kvm__init_ram() for details) PROT_NONE so that
> +			 * if we accidently write to it, we will know.
> +			 */
> +			mprotect(self->ram_start + KVM_32BIT_GAP_START, KVM_32BIT_GAP_SIZE, PROT_NONE);
> +		}
> +	}
>  	if (self->ram_start == MAP_FAILED)
>  		die("out of memory");
>  


-- 
Best Regards,
Asias He