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

[Ilya Leoshkevich]

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?