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

[Ingo Molnar <mingo@elte.hu>]

* Asias He <asias.hejun@gmail.com> wrote:

> 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.

it's useful if you report the 'gcc -v' output for compiler warnings - so that 
we can after some time have a mental picture of which GCC versions produce 
spurious warnings.

Btw,. it would also be useful to add a 'make WERROR=0' option - that way 
warnings that trigger only on some GCC versions can be skipped during the build 
while they will still be reported to us because the default 'make' fails.

[ If you add that then please also send such a patch against tools/perf/ :-) ]

Thanks,

	Ingo