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linux-user: Passthrough MADV_DONTNEED for certain file mappings

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This is a follow-up for commit 892a4f6a75 ("linux-user: Add partial
support for MADV_DONTNEED"), which added passthrough for anonymous
mappings. File mappings can be handled in a similar manner.

In order to do that, mark pages, for which mmap() was passed through,
with PAGE_PASSTHROUGH, and then allow madvise() passthrough for these
pages. Drop the explicit PAGE_ANON check, since anonymous mappings are
expected to have PAGE_PASSTHROUGH anyway.

Add PAGE_PASSTHROUGH to PAGE_STICKY in order to keep it on mprotect().

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220725125043.43048-1-iii@linux.ibm.com>
Message-Id: <20220906000839.1672934-5-iii@linux.ibm.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
This commit is contained in:
Ilya Leoshkevich 2022-09-06 02:08:38 +02:00 • committed by Laurent Vivier
parent 375ce49be2
commit f93b76958a
3 changed files with 29 additions and 6 deletions
Download patch file Download diff file Expand all files Collapse all files

2
accel/tcg/translate-all.c
View file

@ -2258,7 +2258,7 @@ int page_get_flags(target_ulong address)
#ifndef PAGE_TARGET_STICKY #ifndef PAGE_TARGET_STICKY
#define PAGE_TARGET_STICKY 0 #define PAGE_TARGET_STICKY 0
#endif #endif
#define PAGE_STICKY (PAGE_ANON | PAGE_TARGET_STICKY) #define PAGE_STICKY (PAGE_ANON | PAGE_PASSTHROUGH | PAGE_TARGET_STICKY)
/* Modify the flags of a page and invalidate the code if necessary. /* Modify the flags of a page and invalidate the code if necessary.
The flag PAGE_WRITE_ORG is positioned automatically depending The flag PAGE_WRITE_ORG is positioned automatically depending

6
include/exec/cpu-all.h
View file

@ -262,6 +262,12 @@ extern const TargetPageBits target_page;
#define PAGE_TARGET_1 0x0200 #define PAGE_TARGET_1 0x0200
#define PAGE_TARGET_2 0x0400 #define PAGE_TARGET_2 0x0400
/*
* For linux-user, indicates that the page is mapped with the same semantics
* in both guest and host.
*/
#define PAGE_PASSTHROUGH 0x0800
#if defined(CONFIG_USER_ONLY) #if defined(CONFIG_USER_ONLY)
void page_dump(FILE *f); void page_dump(FILE *f);

25
linux-user/mmap.c
View file

@ -431,7 +431,8 @@ abi_ulong mmap_find_vma(abi_ulong start, abi_ulong size, abi_ulong align)
abi_long target_mmap(abi_ulong start, abi_ulong len, int target_prot, abi_long target_mmap(abi_ulong start, abi_ulong len, int target_prot,
int flags, int fd, abi_ulong offset) int flags, int fd, abi_ulong offset)
{ {
abi_ulong ret, end, real_start, real_end, retaddr, host_offset, host_len; abi_ulong ret, end, real_start, real_end, retaddr, host_offset, host_len,
passthrough_start = -1, passthrough_end = -1;
int page_flags, host_prot; int page_flags, host_prot;
mmap_lock(); mmap_lock();
@ -544,6 +545,8 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, int target_prot,
host_start += offset - host_offset; host_start += offset - host_offset;
} }
start = h2g(host_start); start = h2g(host_start);
passthrough_start = start;
passthrough_end = start + len;
} else { } else {
if (start & ~TARGET_PAGE_MASK) { if (start & ~TARGET_PAGE_MASK) {
errno = EINVAL; errno = EINVAL;
@ -626,6 +629,8 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, int target_prot,
host_prot, flags, fd, offset1); host_prot, flags, fd, offset1);
if (p == MAP_FAILED) if (p == MAP_FAILED)
goto fail; goto fail;
passthrough_start = real_start;
passthrough_end = real_end;
} }
} }
the_end1: the_end1:
@ -633,7 +638,18 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, int target_prot,
page_flags |= PAGE_ANON; page_flags |= PAGE_ANON;
} }
page_flags |= PAGE_RESET; page_flags |= PAGE_RESET;
if (passthrough_start == passthrough_end) {
page_set_flags(start, start + len, page_flags); page_set_flags(start, start + len, page_flags);
} else {
if (start < passthrough_start) {
page_set_flags(start, passthrough_start, page_flags);
}
page_set_flags(passthrough_start, passthrough_end,
page_flags | PAGE_PASSTHROUGH);
if (passthrough_end < start + len) {
page_set_flags(passthrough_end, start + len, page_flags);
}
}
the_end: the_end:
trace_target_mmap_complete(start); trace_target_mmap_complete(start);
if (qemu_loglevel_mask(CPU_LOG_PAGE)) { if (qemu_loglevel_mask(CPU_LOG_PAGE)) {
@ -852,7 +868,7 @@ static bool can_passthrough_madv_dontneed(abi_ulong start, abi_ulong end)
} }
for (addr = start; addr < end; addr += TARGET_PAGE_SIZE) { for (addr = start; addr < end; addr += TARGET_PAGE_SIZE) {
if (!(page_get_flags(addr) & PAGE_ANON)) { if (!(page_get_flags(addr) & PAGE_PASSTHROUGH)) {
return false; return false;
} }
} }
@ -894,8 +910,9 @@ abi_long target_madvise(abi_ulong start, abi_ulong len_in, int advice)
* This is a hint, so ignoring and returning success is ok. * This is a hint, so ignoring and returning success is ok.
* *
* This breaks MADV_DONTNEED, completely implementing which is quite * This breaks MADV_DONTNEED, completely implementing which is quite
* complicated. However, there is one low-hanging fruit: host-page-aligned * complicated. However, there is one low-hanging fruit: mappings that are
* anonymous mappings. In this case passthrough is safe, so do it. * known to have the same semantics in the host and the guest. In this case
* passthrough is safe, so do it.
*/ */
mmap_lock(); mmap_lock();
if (advice == TARGET_MADV_DONTNEED && if (advice == TARGET_MADV_DONTNEED &&