[PATCH v3 kvmtool 09/13] builtin_run: Allow standard size specifiers for memory
Alexandru Elisei
alexandru.elisei at arm.com
Wed Jun 1 13:13:27 PDT 2022
Hi,
On Wed, Jun 01, 2022 at 08:39:08PM +0100, Alexandru Elisei wrote:
> Hi,
>
> On Wed, Jun 01, 2022 at 05:14:00PM +0100, Andre Przywara wrote:
> > On Wed, 1 Jun 2022 15:17:50 +0100
> > Alexandru Elisei <alexandru.elisei at arm.com> wrote:
> >
> > Hi Alex,
> >
> > > Hi,
> > >
> > > Thank you for having a look! Replies below.
> > >
> > > On Wed, Jun 01, 2022 at 02:39:55PM +0100, Andre Przywara wrote:
> > > > On Wed, 25 May 2022 12:23:41 +0100
> > > > Alexandru Elisei <alexandru.elisei at arm.com> wrote:
> > > >
> > > > Hi,
> > > >
> > > > > From: Suzuki K Poulose <suzuki.poulose at arm.com>
> > > > >
> > > > > Allow the user to use the standard B (bytes), K (kilobytes), M (megabytes),
> > > > > G (gigabytes), T (terabytes) and P (petabytes) suffixes for memory size.
> > > > > When none are specified, the default is megabytes.
> > > > >
> > > > > Also raise an error if the guest specifies 0 as the memory size, instead
> > > > > of treating it as uninitialized, as kvmtool has done so far.
> > > > >
> > > > > Signed-off-by: Suzuki K Poulose <suzuki.poulose at arm.com>
> > > > > Signed-off-by: Alexandru Elisei <alexandru.elisei at arm.com>
> > > > > ---
> > > > > builtin-run.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++----
> > > > > 1 file changed, 60 insertions(+), 5 deletions(-)
> > > > >
> > > > > diff --git a/builtin-run.c b/builtin-run.c
> > > > > index 2ef159cdb2a3..a49698d5b2fe 100644
> > > > > --- a/builtin-run.c
> > > > > +++ b/builtin-run.c
> > > > > @@ -49,9 +49,11 @@
> > > > > #include <ctype.h>
> > > > > #include <stdio.h>
> > > > >
> > > > > -#define MB_SHIFT (20)
> > > > > #define KB_SHIFT (10)
> > > > > +#define MB_SHIFT (20)
> > > > > #define GB_SHIFT (30)
> > > > > +#define TB_SHIFT (40)
> > > > > +#define PB_SHIFT (50)
> > > >
> > > > Can we lose the parentheses?
> > >
> > > Yes.
> > >
> > > >
> > > > >
> > > > > __thread struct kvm_cpu *current_kvm_cpu;
> > > > >
> > > > > @@ -87,6 +89,60 @@ void kvm_run_set_wrapper_sandbox(void)
> > > > > kvm_run_wrapper = KVM_RUN_SANDBOX;
> > > > > }
> > > > >
> > > > > +static int parse_mem_unit(char **next)
> > > > > +{
> > > > > + int shift = -1;
> > > > > +
> > > > > + switch (**next) {
> > > > > + case 'B': case 'b': shift = 0; break;
> > > > > + case 'K': case 'k': shift = KB_SHIFT; break;
> > > > > + case 'M': case 'm': shift = MB_SHIFT; break;
> > > > > + case 'G': case 'g': shift = GB_SHIFT; break;
> > > > > + case 'T': case 't': shift = TB_SHIFT; break;
> > > > > + case 'P': case 'p': shift = PB_SHIFT; break;
> > > > > + }
> > > > > +
> > > > > + if (shift == -1) {
> > > > > + /* The default is megabytes. */
> > > > > + shift = MB_SHIFT;
> > > >
> > > > Doesn't that look better inside the switch/case?
> > > > default: return MB_SHIFT;
> > >
> > > I think that change alone breaks the logic.
> > >
> > > The code needs to advance next if and only if it matches on one of the
> > > characters. I'll have a go at advancing next in each of the switch arms
> > > above (with the exception of the default one, which I'll add) to see how it
> > > ends up looking.
> >
> > Mmh, but I meant:
> > {
> > switch (**next) {
> > case 'B': case 'b': shift = 0; break;
> > case 'K': case 'k': shift = KB_SHIFT; break;
> > case 'M': case 'm': shift = MB_SHIFT; break;
> > case 'G': case 'g': shift = GB_SHIFT; break;
> > case 'T': case 't': shift = TB_SHIFT; break;
> > case 'P': case 'p': shift = PB_SHIFT; break;
> > default: return MB_SHIFT;
> > }
> >
> > (*next)++;
> >
> > return shift;
> > }
> >
> > that should solve it, shouldn't it?
> >
> > >
> > > >
> > > > > + } else {
> > > > > + (*next)++;
> > > > > + }
> > > > > +
> > > > > + return shift;
> > > > > +}
> > > > > +
> > > > > +static u64 parse_mem_option(const char *nptr, char **next)
> > > > > +{
> > > > > + u64 shift;
> > > > > + u64 val;
> > > > > +
> > > > > + val = strtoull(nptr, next, 10);
> > > > > + if (errno == ERANGE)
> > > > > + die("Memory too large: %s", nptr);
> > > >
> > > > strtoull does not clear errno if it succeeds, so it retains the
> > > > previous error value. So we would need to set errno to 0 just before
> > > > calling strtoull.
> > >
> > > This was intentional on my part, because I was under the impression that
> > > kvmtool treats all instances where errno != 0 as a fatal error. I think I
> > > was wrong about that, I see at least one instance when that isn't the case,
> > > in kvm_setup_guest_init -> extract_file. So it isn't a rule that a non-zero
> > > errno is a fatal error.
> > >
> > > I'll change the code to zero errno before calling strtoull.
> >
> > Thanks!
> >
> > >
> > > >
> > > > > + shift = parse_mem_unit(next);
> > > > > +
> > > > > + if ((val << shift) < val)
> > > > > + die("Memory too large: %s", nptr);
> > > > > +
> > > > > + return val << shift;
> > > > > +}
> > > > > +
> > > > > +static int mem_parser(const struct option *opt, const char *arg, int unset)
> > > > > +{
> > > > > + struct kvm *kvm = opt->ptr;
> > > > > + char *next;
> > > > > +
> > > > > + kvm->cfg.ram_size = parse_mem_option(arg, &next);
> > > > > + if (kvm->cfg.ram_size == 0)
> > > > > + die("Invalid RAM size: %s", arg);
> > > >
> > > > Does 0 hold any significant value (anymore)? I think we die() if we
> > > > encounter invalid values in parse_mem_option()?
> > >
> > > strtoull does not consider an error to convert the string "0" to an
> > > unsigned long long.
> >
> > I was wondering if we treat 0 as an indicator of a conversion error, or as
> > a too-low memory size value here. I don't think we should special case the
>
> It's both. It's an error because (man 2 strotoull, cherry-pick to prove my
> point):
>
> "If there were no digits at all, strtoul() stores the original value of
> nptr in *endptr (and returns 0)"
>
> As for the second part, I'm not sure how setting the size of the VM memory
> to 0 can be considered anything else but an error. I am willing to be
> convinced otherwise though.
>
> > latter, as even 1MB or 2MB are typically too low values for a "normal"
> > kvmtool run ("Fatal: kernel image too big to contain in guest memory.").
> > On the other hand, with --firmware I think we can run a (admittedly very
> > limited) guest with 0MB of RAM.
>
> That leaves us with the rather interesting question of how the firmware
> image can fit in RAM if the size of the RAM is 0. It looks to me like
> kvm__load_firmware should fail in this situation.
>
> >
> > So if we care about garbage as an argument, we should do it by the book
> > (strtoul manpage), and compare the next pointer to the input string
>
> I believe my approach is by the man page, where strotoull returns ERANGE on
> overflow, and 0 if no valid numbers are found. Care to point out what I am
> missing?
Did some thinking, and I think I understand where you're coming from: the
comparison against 0 serves both to check for invalid user input and as a
logical condition for the correct flow of the program.
That's not ideal, as in the future kvmtool might allow 0 as a valid
address. I'll split the two checks, and move the check for valid input to
parse_mem_option, and do it like you suggested (and as is described in the
man page).
Thanks,
Alex
>
> Thanks,
> Alex
>
> > address, plus checking for the returned value being 0, so that
> > "-m gimme-all" is explicitly denied. But that would need to happen in
> > parse_mem_option(), I think, not here.
> >
> > If we cannot be asked, that's probably fine, but I just wanted to
> > check this.
> >
> > Cheers,
> > Andre
> >
> > > > > +
> > > > > + if (*next != '\0')
> > > > > + die("Invalid memory specifier: %s", arg);
> > > > > +
> > > > > + return 0;
> > > > > +}
> > > > > +
> > > > > #ifndef OPT_ARCH_RUN
> > > > > #define OPT_ARCH_RUN(...)
> > > > > #endif
> > > > > @@ -97,8 +153,9 @@ void kvm_run_set_wrapper_sandbox(void)
> > > > > OPT_STRING('\0', "name", &(cfg)->guest_name, "guest name", \
> > > > > "A name for the guest"), \
> > > > > OPT_INTEGER('c', "cpus", &(cfg)->nrcpus, "Number of CPUs"), \
> > > > > - OPT_U64('m', "mem", &(cfg)->ram_size, "Virtual machine memory" \
> > > > > - " size in MB."), \
> > > > > + OPT_CALLBACK('m', "mem", NULL, "size[BKMGTP]", \
> > > > > + "Virtual machine memory size, by default measured" \
> > > > > + " in megabytes (M)", mem_parser, kvm), \
> > > > > OPT_CALLBACK('d', "disk", kvm, "image or rootfs_dir", "Disk " \
> > > > > " image or rootfs directory", img_name_parser, \
> > > > > kvm), \
> > > > > @@ -522,8 +579,6 @@ static void kvm_run_validate_cfg(struct kvm *kvm)
> > > > > pr_warning("Ignoring initrd file when loading a firmware image");
> > > > >
> > > > > if (kvm->cfg.ram_size) {
> > > > > - /* User specifies RAM size in megabytes. */
> > > > > - kvm->cfg.ram_size <<= MB_SHIFT;
> > > > > available_ram = host_ram_size();
> > > > > if (available_ram && kvm->cfg.ram_size > available_ram) {
> > > > > pr_warning("Guest memory size %lluMB exceeds host physical RAM size %lluMB",
> > > >
> >
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