* [Qemu-devel] [PATCH 2/3] linux-user: Fix shmat emulation by honoring host SHMLBA
2018-10-17 1:54 [Qemu-devel] [PATCH 0/3] linux-user: Fix shmat by honoring SHMLBA Richard Henderson
2018-10-17 1:54 ` [Qemu-devel] [PATCH 1/3] tests/tcg/multiarch/linux-test: Fix error check for shmat Richard Henderson
@ 2018-10-17 1:54 ` Richard Henderson
2018-10-17 1:54 ` [Qemu-devel] [PATCH 3/3] linux-user: Align mmap_find_vma to host page size Richard Henderson
2 siblings, 0 replies; 4+ messages in thread
From: Richard Henderson @ 2018-10-17 1:54 UTC (permalink / raw)
To: qemu-devel; +Cc: laurent
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>
---
linux-user/qemu.h | 2 +-
linux-user/elfload.c | 17 +++++-----
linux-user/mmap.c | 74 +++++++++++++++++++++++---------------------
linux-user/syscall.c | 3 +-
4 files changed, 52 insertions(+), 44 deletions(-)
diff --git a/linux-user/qemu.h b/linux-user/qemu.h
index b4959e41c6..67a4f3c020 100644
--- a/linux-user/qemu.h
+++ b/linux-user/qemu.h
@@ -439,7 +439,7 @@ 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);
diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 10bca65b99..ec200a39ad 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -3,6 +3,7 @@
#include <sys/param.h>
#include <sys/resource.h>
+#include <sys/shm.h>
#include "qemu.h"
#include "disas/disas.h"
@@ -1942,6 +1943,8 @@ 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;
@@ -1959,7 +1962,7 @@ 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;
@@ -1995,8 +1998,8 @@ 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;
@@ -2009,7 +2012,7 @@ 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;
}
@@ -2036,7 +2039,7 @@ 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: [ ][ ][ ][ ][ ]
@@ -2064,7 +2067,7 @@ 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;
}
@@ -2101,7 +2104,7 @@ 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.
diff --git a/linux-user/mmap.c b/linux-user/mmap.c
index 41e0983ce8..47950ee9d7 100644
--- a/linux-user/mmap.c
+++ b/linux-user/mmap.c
@@ -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;
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index ae3c0dfef7..7a69855344 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -3815,7 +3815,8 @@ 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;
--
2.17.2
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