[v3] linux-user: Improve host and guest page size handling

[PATCH v3 05/33] linux-user/hppa: Simplify init_guest_commpage

Posted by Richard Henderson 10 months, 4 weeks ago

If reserved_va, then we have already reserved the entire
guest virtual address space; no need to remap page.
If !reserved_va, then use MAP_FIXED_NOREPLACE.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 linux-user/elfload.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index c166faabab..96d8d4f84c 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -1969,16 +1969,21 @@ static inline void init_thread(struct target_pt_regs *regs,
 
 static bool init_guest_commpage(void)
 {
-    void *want = g2h_untagged(LO_COMMPAGE);
-    void *addr = mmap(want, qemu_host_page_size, PROT_NONE,
-                      MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, -1, 0);
+    /* If reserved_va, then we have already mapped 0 page on the host. */
+    if (!reserved_va) {
+        int host_page_size = qemu_real_host_page_size();
+        void *want, *addr;
 
-    if (addr == MAP_FAILED) {
-        perror("Allocating guest commpage");
-        exit(EXIT_FAILURE);
-    }
-    if (addr != want) {
-        return false;
+        want = g2h_untagged(LO_COMMPAGE);
+        addr = mmap(want, host_page_size, PROT_NONE,
+                    MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED_NOREPLACE, -1, 0);
+        if (addr == MAP_FAILED) {
+            perror("Allocating guest commpage");
+            exit(EXIT_FAILURE);
+        }
+        if (addr != want) {
+            return false;
+        }
     }
 
     /*
-- 
2.34.1

Re: [PATCH v3 05/33] linux-user/hppa: Simplify init_guest_commpage

Posted by Ilya Leoshkevich 10 months ago

On Tue, Jan 02, 2024 at 12:57:40PM +1100, Richard Henderson wrote:
> If reserved_va, then we have already reserved the entire
> guest virtual address space; no need to remap page.
> If !reserved_va, then use MAP_FIXED_NOREPLACE.
> 
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  linux-user/elfload.c | 23 ++++++++++++++---------
>  1 file changed, 14 insertions(+), 9 deletions(-)
> 
> diff --git a/linux-user/elfload.c b/linux-user/elfload.c
> index c166faabab..96d8d4f84c 100644
> --- a/linux-user/elfload.c
> +++ b/linux-user/elfload.c
> @@ -1969,16 +1969,21 @@ static inline void init_thread(struct target_pt_regs *regs,
>  
>  static bool init_guest_commpage(void)
>  {
> -    void *want = g2h_untagged(LO_COMMPAGE);
> -    void *addr = mmap(want, qemu_host_page_size, PROT_NONE,
> -                      MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, -1, 0);
> +    /* If reserved_va, then we have already mapped 0 page on the host. */
> +    if (!reserved_va) {
> +        int host_page_size = qemu_real_host_page_size();
> +        void *want, *addr;
>  
> -    if (addr == MAP_FAILED) {
> -        perror("Allocating guest commpage");
> -        exit(EXIT_FAILURE);
> -    }
> -    if (addr != want) {
> -        return false;
> +        want = g2h_untagged(LO_COMMPAGE);
> +        addr = mmap(want, host_page_size, PROT_NONE,
> +                    MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED_NOREPLACE, -1, 0);
> +        if (addr == MAP_FAILED) {
> +            perror("Allocating guest commpage");
> +            exit(EXIT_FAILURE);
> +        }
> +        if (addr != want) {
> +            return false;
> +        }
>      }
>  
>      /*
> -- 
> 2.34.1

Reviewed-by: Ilya Leoshkevich <iii@linux.ibm.com>

Re: Re: [PATCH v3 05/33] linux-user/hppa: Simplify init_guest_commpage

Posted by Ilya Leoshkevich 10 months ago

On Mon, Jan 29, 2024 at 11:28:59AM +0100, Ilya Leoshkevich wrote:
> On Tue, Jan 02, 2024 at 12:57:40PM +1100, Richard Henderson wrote:
> > If reserved_va, then we have already reserved the entire
> > guest virtual address space; no need to remap page.
> > If !reserved_va, then use MAP_FIXED_NOREPLACE.
> > 
> > Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> > ---
> >  linux-user/elfload.c | 23 ++++++++++++++---------
> >  1 file changed, 14 insertions(+), 9 deletions(-)
> > 
> > diff --git a/linux-user/elfload.c b/linux-user/elfload.c
> > index c166faabab..96d8d4f84c 100644
> > --- a/linux-user/elfload.c
> > +++ b/linux-user/elfload.c
> > @@ -1969,16 +1969,21 @@ static inline void init_thread(struct target_pt_regs *regs,
> >  
> >  static bool init_guest_commpage(void)
> >  {
> > -    void *want = g2h_untagged(LO_COMMPAGE);
> > -    void *addr = mmap(want, qemu_host_page_size, PROT_NONE,
> > -                      MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, -1, 0);
> > +    /* If reserved_va, then we have already mapped 0 page on the host. */
> > +    if (!reserved_va) {
> > +        int host_page_size = qemu_real_host_page_size();
> > +        void *want, *addr;
> >  
> > -    if (addr == MAP_FAILED) {
> > -        perror("Allocating guest commpage");
> > -        exit(EXIT_FAILURE);
> > -    }
> > -    if (addr != want) {
> > -        return false;
> > +        want = g2h_untagged(LO_COMMPAGE);
> > +        addr = mmap(want, host_page_size, PROT_NONE,
> > +                    MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED_NOREPLACE, -1, 0);

One question though: if TARGET_PAGE_SIZE > host_page_size, things would
work, because the magic offsets are quite small. But wouldn't it be
overall cleaner to map TARGET_PAGE_SIZE bytes, just to be closer to the
real thing?

Re: [PATCH v3 05/33] linux-user/hppa: Simplify init_guest_commpage

Posted by Pierrick Bouvier 10 months, 3 weeks ago

On 1/2/24 05:57, Richard Henderson wrote:
> If reserved_va, then we have already reserved the entire
> guest virtual address space; no need to remap page.
> If !reserved_va, then use MAP_FIXED_NOREPLACE.
> 
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>   linux-user/elfload.c | 23 ++++++++++++++---------
>   1 file changed, 14 insertions(+), 9 deletions(-)
> 
> diff --git a/linux-user/elfload.c b/linux-user/elfload.c
> index c166faabab..96d8d4f84c 100644
> --- a/linux-user/elfload.c
> +++ b/linux-user/elfload.c
> @@ -1969,16 +1969,21 @@ static inline void init_thread(struct target_pt_regs *regs,
>   
>   static bool init_guest_commpage(void)
>   {
> -    void *want = g2h_untagged(LO_COMMPAGE);
> -    void *addr = mmap(want, qemu_host_page_size, PROT_NONE,
> -                      MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, -1, 0);
> +    /* If reserved_va, then we have already mapped 0 page on the host. */
> +    if (!reserved_va) {
> +        int host_page_size = qemu_real_host_page_size();
> +        void *want, *addr;
>   
> -    if (addr == MAP_FAILED) {
> -        perror("Allocating guest commpage");
> -        exit(EXIT_FAILURE);
> -    }
> -    if (addr != want) {
> -        return false;
> +        want = g2h_untagged(LO_COMMPAGE);
> +        addr = mmap(want, host_page_size, PROT_NONE,
> +                    MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED_NOREPLACE, -1, 0);
> +        if (addr == MAP_FAILED) {
> +            perror("Allocating guest commpage");
> +            exit(EXIT_FAILURE);
> +        }
> +        if (addr != want) {
> +            return false;
> +        }
>       }
>   
>       /*

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>