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linux-user: Fix shmat emulation by honoring host SHMLBA

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For those hosts with SHMLBA > getpagesize, we don't automatically
select a guest address that is compatible with the host.  We can
achieve this by boosting the alignment of guest_base and by adding
an extra alignment argument to mmap_find_vma.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20190519201953.20161-13-richard.henderson@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
This commit is contained in:
Richard Henderson 2019-05-19 13:19:52 -07:00 committed by Laurent Vivier
parent abcac736c1
commit 30ab9ef296
4 changed files with 52 additions and 44 deletions
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17
linux-user/elfload.c
View File

@ -3,6 +3,7 @@
#include <sys/param.h>
#include <sys/resource.h>
#include <sys/shm.h>
#include "qemu.h"
#include "disas/disas.h"
@ -2012,6 +2013,8 @@ unsigned long init_guest_space(unsigned long host_start,
unsigned long guest_start,
bool fixed)
{
/* In order to use host shmat, we must be able to honor SHMLBA. */
unsigned long align = MAX(SHMLBA, qemu_host_page_size);
unsigned long current_start, aligned_start;
int flags;
@ -2029,7 +2032,7 @@ unsigned long init_guest_space(unsigned long host_start,
}
/* Setup the initial flags and start address. */
current_start = host_start & qemu_host_page_mask;
current_start = host_start & -align;
flags = MAP_ANONYMOUS | MAP_PRIVATE | MAP_NORESERVE;
if (fixed) {
flags |= MAP_FIXED;
@ -2065,8 +2068,8 @@ unsigned long init_guest_space(unsigned long host_start,
return (unsigned long)-1;
}
munmap((void *)real_start, host_full_size);
if (real_start & ~qemu_host_page_mask) {
/* The same thing again, but with an extra qemu_host_page_size
if (real_start & (align - 1)) {
/* The same thing again, but with extra
* so that we can shift around alignment.
*/
unsigned long real_size = host_full_size + qemu_host_page_size;
@ -2079,7 +2082,7 @@ unsigned long init_guest_space(unsigned long host_start,
return (unsigned long)-1;
}
munmap((void *)real_start, real_size);
real_start = HOST_PAGE_ALIGN(real_start);
real_start = ROUND_UP(real_start, align);
}
current_start = real_start;
}
@ -2106,7 +2109,7 @@ unsigned long init_guest_space(unsigned long host_start,
}
/* Ensure the address is properly aligned. */
if (real_start & ~qemu_host_page_mask) {
if (real_start & (align - 1)) {
/* Ideally, we adjust like
*
* pages: [ ][ ][ ][ ][ ]
@ -2134,7 +2137,7 @@ unsigned long init_guest_space(unsigned long host_start,
if (real_start == (unsigned long)-1) {
return (unsigned long)-1;
}
aligned_start = HOST_PAGE_ALIGN(real_start);
aligned_start = ROUND_UP(real_start, align);
} else {
aligned_start = real_start;
}
@ -2171,7 +2174,7 @@ unsigned long init_guest_space(unsigned long host_start,
* because of trouble with ARM commpage setup.
*/
munmap((void *)real_start, real_size);
current_start += qemu_host_page_size;
current_start += align;
if (host_start == current_start) {
/* Theoretically possible if host doesn't have any suitably
* aligned areas. Normally the first mmap will fail.

74
linux-user/mmap.c
View File

@ -202,49 +202,52 @@ unsigned long last_brk;
/* Subroutine of mmap_find_vma, used when we have pre-allocated a chunk
of guest address space. */
static abi_ulong mmap_find_vma_reserved(abi_ulong start, abi_ulong size)
static abi_ulong mmap_find_vma_reserved(abi_ulong start, abi_ulong size,
abi_ulong align)
{
abi_ulong addr;
abi_ulong end_addr;
abi_ulong addr, end_addr, incr = qemu_host_page_size;
int prot;
int looped = 0;
bool looped = false;
if (size > reserved_va) {
return (abi_ulong)-1;
}
size = HOST_PAGE_ALIGN(size);
end_addr = start + size;
if (end_addr > reserved_va) {
end_addr = reserved_va;
}
addr = end_addr - qemu_host_page_size;
/* Note that start and size have already been aligned by mmap_find_vma. */
end_addr = start + size;
if (start > reserved_va - size) {
/* Start at the top of the address space. */
end_addr = ((reserved_va - size) & -align) + size;
looped = true;
}
/* Search downward from END_ADDR, checking to see if a page is in use. */
addr = end_addr;
while (1) {
addr -= incr;
if (addr > end_addr) {
if (looped) {
/* Failure. The entire address space has been searched. */
return (abi_ulong)-1;
}
end_addr = reserved_va;
addr = end_addr - qemu_host_page_size;
looped = 1;
continue;
/* Re-start at the top of the address space. */
addr = end_addr = ((reserved_va - size) & -align) + size;
looped = true;
} else {
prot = page_get_flags(addr);
if (prot) {
/* Page in use. Restart below this page. */
addr = end_addr = ((addr - size) & -align) + size;
} else if (addr && addr + size == end_addr) {
/* Success! All pages between ADDR and END_ADDR are free. */
if (start == mmap_next_start) {
mmap_next_start = addr;
}
return addr;
}
}
prot = page_get_flags(addr);
if (prot) {
end_addr = addr;
}
if (addr && addr + size == end_addr) {
break;
}
addr -= qemu_host_page_size;
}
if (start == mmap_next_start) {
mmap_next_start = addr;
}
return addr;
}
/*
@ -253,7 +256,7 @@ static abi_ulong mmap_find_vma_reserved(abi_ulong start, abi_ulong size)
* It must be called with mmap_lock() held.
* Return -1 if error.
*/
abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size)
abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size, abi_ulong align)
{
void *ptr, *prev;
abi_ulong addr;
@ -265,11 +268,12 @@ abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size)
} else {
start &= qemu_host_page_mask;
}
start = ROUND_UP(start, align);
size = HOST_PAGE_ALIGN(size);
if (reserved_va) {
return mmap_find_vma_reserved(start, size);
return mmap_find_vma_reserved(start, size, align);
}
addr = start;
@ -299,7 +303,7 @@ abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size)
if (h2g_valid(ptr + size - 1)) {
addr = h2g(ptr);
if ((addr & ~TARGET_PAGE_MASK) == 0) {
if ((addr & (align - 1)) == 0) {
/* Success. */
if (start == mmap_next_start && addr >= TASK_UNMAPPED_BASE) {
mmap_next_start = addr + size;
@ -313,12 +317,12 @@ abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size)
/* Assume the result that the kernel gave us is the
first with enough free space, so start again at the
next higher target page. */
addr = TARGET_PAGE_ALIGN(addr);
addr = ROUND_UP(addr, align);
break;
case 1:
/* Sometimes the kernel decides to perform the allocation
at the top end of memory instead. */
addr &= TARGET_PAGE_MASK;
addr &= -align;
break;
case 2:
/* Start over at low memory. */
@ -416,7 +420,7 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, int prot,
if (!(flags & MAP_FIXED)) {
host_len = len + offset - host_offset;
host_len = HOST_PAGE_ALIGN(host_len);
start = mmap_find_vma(real_start, host_len);
start = mmap_find_vma(real_start, host_len, TARGET_PAGE_SIZE);
if (start == (abi_ulong)-1) {
errno = ENOMEM;
goto fail;
@ -710,7 +714,7 @@ abi_long target_mremap(abi_ulong old_addr, abi_ulong old_size,
} else if (flags & MREMAP_MAYMOVE) {
abi_ulong mmap_start;
mmap_start = mmap_find_vma(0, new_size);
mmap_start = mmap_find_vma(0, new_size, TARGET_PAGE_SIZE);
if (mmap_start == -1) {
errno = ENOMEM;

2
linux-user/qemu.h
View File

@ -443,7 +443,7 @@ abi_long target_mremap(abi_ulong old_addr, abi_ulong old_size,
abi_ulong new_addr);
extern unsigned long last_brk;
extern abi_ulong mmap_next_start;
abi_ulong mmap_find_vma(abi_ulong, abi_ulong);
abi_ulong mmap_find_vma(abi_ulong, abi_ulong, abi_ulong);
void mmap_fork_start(void);
void mmap_fork_end(int child);

3
linux-user/syscall.c
View File

@ -3912,7 +3912,8 @@ static inline abi_ulong do_shmat(CPUArchState *cpu_env,
else {
abi_ulong mmap_start;
mmap_start = mmap_find_vma(0, shm_info.shm_segsz);
/* In order to use the host shmat, we need to honor host SHMLBA. */
mmap_start = mmap_find_vma(0, shm_info.shm_segsz, MAX(SHMLBA, shmlba));
if (mmap_start == -1) {
errno = ENOMEM;